Fuel cell and membrane electrode assembly

ABSTRACT

A fuel cell has an anode, a cathode, and a polymer electrolyte membrane placed between the anode and the cathode. The anode includes a catalyst which is composed of binary or ternary particulates deposited on a carbon support. The particulate is represented by a general formula: Pt—P, wherein Ru is optionally present. The content of P is in a range of 2 mol % to 50 mol % based on the total moles of Pt or Pt—Ru. The diameter of the catalyst particulates is in range from 1 to 3 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a Continuation-in-Part (CIP) application ofcommonly-assigned, co-pending, U.S. patent application Ser. No.11/017,825 filed Dec. 22, 2004 and Ser. No. 11/268,503 filed Nov. 8,2005 which are both hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fuel cells and membrane electrodeassemblies having a new catalyst at an electrode. More specifically, thepresent invention relates to fuel cells and membrane electrodeassemblies comprising a platinum and phosphorus catalyst at either afuel electrode/anode or cathode.

2. Description of Related Art

For the most part, electric energy has been supplied by thermal powergeneration, water power generation, and nuclear electric powergeneration. However, thermal power generation burns fossil fuels such asoil and coal and it causes not only extensive environmental pollutionbut also a depletion of energy resources such as oil. The use of waterpower generation requires large-scale dam construction so that thenumber of sites for proper construction are limited. Also, the buildingof the dam and the change in water coverage of the land can causedestruction of nature. Further, the nuclear electric power generationhas problems including the fact that radioactive contamination ispossible in the event of an accident which can be fatal anddecommissioning of nuclear reactor facility is difficult. These problemshave resulted in the decrease of nuclear reactor construction on aglobal basis.

As a power generation system which does not require a large-scalefacility nor causes environmental pollution, wind power generation andsolar photovoltaic power generation have come into use around the world.Wind power generation and solar photovoltaic power generation have comeinto practical use in some places. However, wind power generation cannotgenerate power with no wind and the solar photovoltaic power generationcannot generate power with no sunlight. The two systems are dependent onnatural phenomena, and thus, are incapable of providing a stable powersupply. Further, the wind power generation has a problem that thefrequency of generated power varies with the intensity of wind, causingbreakdown of the electrical equipment.

Recently, a power plant that draws electrical energy from hydrogenenergy, such as hydrogen fuel cells, has been under active development.The hydrogen is obtained by splitting water and exists inexhaustibly onthe earth. In addition, the hydrogen has a large chemical energy amountper unit mass, and it does not generate hazardous substances and globalwarming gases when used as an energy source.

A fuel cell which uses methanol instead of hydrogen has also beenstudied actively. A methanol fuel cell directly uses methanol, which isa liquid fuel, is easy to use and is low in cost. Thus, the methanolfuel cell is expected to be used as a relatively small output powersource for household or industrial use. A theoretical output voltage ofa methanol/oxygen fuel cell is 1.2 V (25° C.), which is almost the sameas that of the hydrogen fuel cell. Thus, they could have the same enduses in principle.

A solid-polyelectrolyte fuel cell and a direct methanol fuel celloxidize hydrogen or methanol at the anode and reduce oxygen at thecathode, thereby drawing electric energy. Since the oxidation-reductionreaction has a high thermodynamic barrier making it difficult to achieveat room temperature, a catalyst is used in the fuel cells. Initial fuelcells use platinum (Pt) as a catalyst, depositing it on a carbonsupport. The Pt has catalytic activity for oxidation of hydrogen andmethanol. A conventional approach for minimizing Pt catalyst particlesto increase a reactive surface area is to control the depositionatmosphere of the Pt catalyst by adjusting external factors in thedeposition process. For example, Japanese Unexamined Patent ApplicationPublication No. 56-155645 introduces a technique that, when reducing Ption by adding alcohol and depositing it on a carbon support, addspolyvinyl alcohol into a reaction solvent. The polyvinyl alcohol servesas an organic protective agent, which absorbs weakly onto the surface ofthe Pt catalyst particles, thereby forming fine Pt catalystparticulates. However, since the organic protective agent absorbs ontothe surface of the Pt catalyst in this technique, it is necessary toremove the organic protective agent from the surface of the Pt catalystto show its catalytic activity. The heat treatment at 400° C. in theatmosphere of hydrogen gas, which follows the generation of the Ptparticulates, is proposed to remove the organic protective agent.However, this treatment cannot completely remove the organic protectiveagent from the Pt catalyst surface. This inhibits the Pt catalystactivity. Further, the heat treatment at 400° C. can cause sintering ofthe Pt particulates, which results in an increase in the catalystparticle size and a decrease in the catalytic activity.

Furthermore, it is possible for chemisorption to occur of carbonmonoxide (CO) generated during the methanol oxidation process orcontained in the hydrogen gas onto the Pt catalyst at the anode, whichresults in deactivation of catalytic activity. This is referred to ascatalyst poisoning by CO. In order to suppress the Pt catalyst poisoningby CO, an additive element into the Pt has been searched, and it wasfound that adding Ru to Pt significantly reduces the catalyst poisoningby CO (see Japanese Unexamined Patent Application Publication No.57-5266, for example) at the anode.

Though the Ru itself does not oxidize hydrogen and methanol, it servesas a promoter that quickly oxidizes CO deposited on Pt into CO₂ andreleases it. In the case of a direct methanol fuel cell, for example, adeprotonation reaction occurs on the Pt catalyst particles and COchemically adsorbs onto the Pt catalyst particles, as indicated by thefollowing reaction formula (1). This is the catalyst poisoning by CO.However, with the use of a Pt—Ru catalyst containing Ru, the Ru reactswith water to generate Ru—OH as indicated by the following reactionformula (2). Then, the CO, which chemically absorbs onto the Pt catalystparticle surface, is oxidized into CO₂ and removed, as indicated by thefollowing reaction formula (3):Pt+CH₃OH→Pt—CO+4H⁺+4e ⁻  (1)Ru+H₂O→Ru—OH+H⁺ +e ⁻  (2)Pt—CO+Ru—OH→Pt+Ru+H⁺ +e ⁻+CO₂↑  (3)

If the Pt—Ru catalyst is synthesized by impregnation, electrolessplating, or alcohol reduction, the particle size falls in the range of 5to 10 nm. If the Pt—Ru particle size remains large, the effectivecatalyst surface area does not increase and the catalytic activity staysunimproved. In order to enhance the catalytic activity of the Pt—Ru, itis effective to reduce the Pt—Ru particle size to below 5 nm andincrease the effective catalyst surface area. In this case, thetechnique of adding the organic protective agent to reduce the Pt—Rucatalyst particle size is not available for the above reasons. A neweffective technique to produce a Pt—Ru catalyst for the anode of lessthan 5 nm has thus been strongly required, but it remains unachieved.

Similarly, a Pt catalyst is used at the cathode of fuel cell. At thecathode, the oxygen is reduced by electrons which are generated at anodeand reacts with protons which come from anode, which generates water bythe following reaction formula (4).O₂+4e ⁻+4H⁺→2H₂O   (4)

In order to enhance the catalytic activity of the Pt, it is alsoeffective to reduce the Pt particle size to below 5 nm and increase theeffective catalyst surface area. In this case, the technique of addingthe organic protective agent to reduce the Pt catalyst particle size isnot available for the above reasons. Anew effective technique to producea Pt catalyst for the cathode less than 5 nm has thus been stronglyrequired, but it remains unachieved.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a fuel cell and a membrane electrode assembly which have a newPt catalyst system with an average particle diameter of less than 5 nmfor use in the anode (fuel electrode) and/or cathode (oxygen electrode).Preferably, average particle diameter is in a range of 1 nm to 3 nm.

In an embodiment of the invention, the catalyst particles comprise Ptand least 2 atom % P. Preferably, the content of P is 2 atom % to 50atom %. More preferably, the content of P is 20 atom % to 35 atom %.

In another embodiment of the invention, the particles have a narrow sizedistribution wherein the particles have an average particle size of lessthan ±15% of the mean average particle size.

In another embodiment of the invention, the heterogeneous catalystfurther comprises a carbon support.

The carbon support is can be any type known in the art, but ispreferably at least one selected from the group consisting of carbonblack (e.g., acetylene black) and carbon nanotube (e.g., multi-walledcarbon nanotube). Preferably, the carbon support has a specific surfacein a range of 20 m²/g to 300 m²/g. More preferably, the carbon supporthas a specific surface in a range of 20 m²/g to 60 m²/g.

According to one aspect of the present invention, there is provided afuel cell which includes a fuel electrode, an oxygen electrode, and apolymer electrolyte membrane which is placed between the fuel electrodeand the oxygen electrode. The fuel electrode and the oxygen electrodeinclude the above-described heterogeneous Pt catalyst system having anaverage particle diameter of less than 5 nm. At the fuel electrode, thecatalyst is preferably a ternary particulate which is deposited on acarbon support, wherein the ternary particulate is represented by ageneral formula: Pt—Ru—P. Whereas at the oxygen electrode, theheterogeneous catalyst is a binary particulate which is deposited on acarbon support, the binary particulate being represented by a generalformula: Pt—P.

In an embodiment of the invention, the ternary particulate comprises upto 60 atom % Ru. Preferably, the ratio of Pt and Ru in the particles isPt₄₀Ru₆₀ to Pt₉₀Ru₁₀. More preferably, the particles comprise at least60 atom % Pt. Most preferably, the content of P is in a range of lessthan 50 atom %.

In an embodiment of the invention, the new Pt system catalyst with anaverage particle diameter of less than 5 nm is used in a fuel cell or amembrane electrode assembly and is made in a process comprising a stepof reducing Pt ions in the presence of a reducing agent comprisingphosphorus. Preferably, the reducing agent is a compound comprisingphosphorus which is at least one of derivatives of phosphinic acid orphosphonic acid(including alkali and ammonium salts).

When the catalyst is to be used at the anode, the process furthercomprises reducing Ru ions with the reducing agent.

In an embodiment of the invention, the process for preparing theheterogeneous catalyst comprises a step of reducing the Pt ions and Ruions with the reducing agent.

In an embodiment of the invention, the reducing step is an alcoholreduction step or electroless plating step. However, it is alsoenvisioned that the reducing step can be an electrolysis step.

An embodiment of the invention is a method of producing a voltage withthe fuel cell comprising the inventive Pt system catalyst having anaverage particle diameter of less than 5 nm, wherein said methodcomprises feeding methanol and water to the anode and feeding oxygen tothe cathode.

An embodiment of the invention is a membrane electrode assembly,comprising a fuel electrode catalyst layer, an oxygen electrode catalystlayer and a polymer electrolyte membrane placed between the fuelelectrode catalyst layer and the oxygen electrode catalyst layer whereinsaid fuel electrode catalyst layer and/or oxygen electrode catalystlayer comprise the inventive Pt system catalyst having an averageparticle diameter of less than 5 nm. The present invention adds P-atomsto a Pt catalyst which may further contain Ru to form a binary orternary catalyst when depositing the Pt or Pt—Ru particulates on acarbon support by electroless plating or alcohol reduction. Thisminiaturizes the catalyst deposited on the carbon support by the actionof P from outside and inside the particle, which increases the surfacearea of the catalyst, thereby improving catalytic activity, and whenpresent, maintaining the effect of adding Ru. Further, the presentinventors have found that, though NAFION® membrane, available from E.I.DuPont de Nemours and Company, is generally used as a polymerelectrolyte membrane between the anode and cathode of the fuel cell, theuse of the NAFION® membrane causes a hydrogen atom of a sulfonic groupto turn into H⁺ to exert proton conductivity. This makes the boundarybetween the NAFION® membrane and the electrode catalyst strongly acidic.While metallic elements from group III such as Mo, Mn, Fe, and Co arenot acid-resistant and subject to transformation with H⁺, P is differentfrom other metallic elements from group III elements and isacid-resistant, thus being suitable for use as an additional element toa catalyst for a fuel cell.

The present invention have found that adding P to produce Pt—P catalystwhen depositing Pt catalyst on a carbon support by electroless plating,alcohol reduction, or ultrasonic reduction miniaturizes Pt catalystparticles that are deposited on the carbon support by the action of Pfrom the inside and outside of the Pt catalyst particles, whichincreases the specific surface area of the catalyst particles, therebyimproving catalytic activity.

The above and other objects, features and advantages of the presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a Pt—Ru—P catalyst particulatesynthesized by an alcohol reduction method according to the presentinvention;

FIG. 2 is a schematic sectional view of a Pt—Ru—P catalyst particulatesynthesized by an electroless plating method according to the presentinvention;

FIG. 3A shows an electron microscopic image of the Pt—Ru—P particulatecatalyst on the carbon support of the example 1;

FIG. 3B shows the Pt—Ru particulate catalyst on the carbon support ofthe comparative example 1;

FIG. 4 is a partial schematic block diagram of an example of a directmethanol fuel cell;

FIG. 5 is a partial schematic block diagram of an example of a polymerelectrolyte fuel cell;

FIG. 6A is an electron microscope image of the Pt—Ru—P catalyst on amulti-walled carbon nanotube support of the example 20;

FIG. 6B is an electron microscope image of the Pt—Ru catalyst on amulti-walled carbon nanotube support of comparative example 13;

FIG. 7A shows a transmission electron microscope image of PtP catalystwith a multiwalled carbon nanotube support; and

FIG. 7B shows a transmission electron microscope image of Pt catalystwith a multiwalled carbon nanotube support.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A catalyst for a fuel cell of the present invention includes aparticulate for an anode or cathode comprising platinum and phosphoruswhich are deposited on a carbon support. When the particulate is used atthe anode, it preferably further includes ruthenium.

In the above formula, a content of P is preferably 2 to 50 mol % of thetotal moles of Pt—Ru. If the content of P is less than 2 mol %, it failsin attaining expected effects. If, on the other hand, the content of Pis more than 50 mol %, the content of Pt—Ru is too small, causingadverse effects on cell outputs. More preferably, the content of P is 5to 30 mol %.

An atomic ratio (at. %) of Pt and Ru in the above ternary catalyst ispreferably in the range of 40:60 to 90:10. If Ru is less than 10 at %,it causes disadvantages such as insufficient prevention of CO poisoning.If, on the other hand, Pt is less than 40 at %, it causes insufficientcatalytic activity for methanol oxidation.

Setting the atomic composition of Pt—Ru to Pt₄₀—Ru₆₀ to Pt₉₀—Ru₁₀ allowsthe composition of the outermost surface of the catalyst to be optimizedso as to enhance the catalytic activity. Further, setting the Pcomposition to 2 to 50 mol % of the total moles of Pt—Ru allowssuppressing the particle growth of the Pt or Pt—Ru catalyst so as toproduce a catalyst with a large specific surface. In this condition, thereactions of the formulas (2) and (3) proceed more rapidly, therebyimproving oxidation activity of methanol.

The average particle size of the Pt—P and Pt—Ru—P catalysts ispreferably 1 to 3 nm. If the particle size is less than 1 nm, theactivity on a synthesized catalyst surface is too high, and the catalystforms a chemical compound on its surface layer together with a substanceexisting in the vicinity, thus decreasing its own activity. If, on theother hand, the particle size is more than 3 nm, it is impossible tosufficiently increase the catalyst surface area per unit weight, thusfailing to enhance the catalytic activity.

The specific surface area of the carbon support which serves as acarrier of the catalyst is preferably 20 to 300 m²/g. If the specificsurface area is less than 20 m²/g, the carbon support cannot support thecatalyst sufficiently. If, on the other hand, it is more than 300 m²/g,the number of pores existing in the carbon support is too large and thesize of the pores is too small, which increases the number of catalystparticles to be buried in the pores. The catalysts buried in the poreshardly create proper three-phase interfaces (where the metal atoms arein contact with both the fuel and NAFION®) in the cell reaction andcease to function as a catalyst. In addition, as the specific surfacearea of the carbon support increases, bulk density (in the unit ofgram/1000 ml) tends to increase. If a catalyst having the same loadingrate (for example, 50 wt %) is deposited on a different carbon supportwith different bulk density, the thickness of an electrode changes inspite of the same catalyst application quantity (for example, 5 mg/cm²).Use of a catalyst with a larger bulk density results in a thinnerelectrode. This decreases permeability of fuel at fuel electrode andvolatility of water at the oxygen electrode due to the lack of physicalapertures in the electrodes, deteriorating the cell characteristics.Hence, it is preferred to use a carbon support with a possibly lowestbulk density or smallest specific surface for the carbon support of afuel cell. The carbon support available in the present invention is atleast one of carbon black such as acetylene black, carbon nanotube, orthe like. The carbon nanotube can be single or multi-walled. Preferably,when the carbon support comprises carbon nanotubes, the carbon nanotubesare multi-walled carbon nanotubes. The carbon support may be usedindependently or in combination.

The Pt—Ru—P catalyst of the present invention is particularly suitablefor use as a catalyst of a fuel electrode such as a methanol electrodeof a direct methanol fuel cell (DMFC) and a hydrogen electrode of apolymer electrolyte fuel cell (PEFC).

The Pt—Ru—P catalyst particulates of the present invention may beproduced by electroless plating method or alcohol reduction method.

A method of producing the Pt—Ru—P catalyst particulates of thisinvention by the alcohol reduction basically comprises (1) a step ofdispersing a carbon support into an organic solvent comprising of one ormore types of alcohol, (2) a step of dissolving Pt salt or complex, Rusalt or complex, and P-containing compound into the alcohol organicsolvent with the dispersed carbon support, (3) a step of adjusting thepH value of the alcohol solvent with dispersed carbon powder to fall inappropriate value, (4) a step of performing heat reflux with alcohol ininert atmosphere, and optionally (5) a step of washing with an alcohol.The catalyst for a fuel cell with the ternary particulates representedby the general formula Pt—Ru—P deposited on the carbon support isthereby generated.

The method of producing the Pt—P catalyst particulates of this inventionby the alcohol reduction, proceeds essentially the same as the method ofproducing the Pt—Ru—P catalyst except that the ruthenium salt or comlexis not used.

A method of producing the Pt—Ru—P catalyst particulates of thisinvention by the electroless plating basically comprises (1) a step ofdispersing a carbon support into a water, (2) a step of dissolving Ptsalt or complex, Ru salt or complex, and P-containing compound into thewater with the dispersed carbon support, (3) a step of adjusting the pHvalue of the water with dispersed carbon powder to fall in appropriatevalue, and (4) a step of performing electroless plating in theatmosphere or inert atmosphere. The catalyst for a fuel cell with theternary particulates represented by the general formula Pt—Ru—Pdeposited on the carbon support is thereby generated.

The method of producing the Pt—P catalyst particulates of this inventionby the electroless plating, proceeds essentially the same as the methodof producing the Pt—Ru—P catalyst except that the ruthenium salt orcomplex is not used.

A method of producing the PtP catalyst of this invention by ultrasonicreduction basically includes: (1) a step of dispersing a carbon supporthaving a specific surface area of 20 m²/g to 300 m²/g into pure water,(2) a step of dissolving Pt salt or complex and P-containing compoundinto the solution containing the dispersed carbon support, (3) a step ofadjusting the pH value of the solution containing the dispersed carbonsupport, the Pt salt or complex and the P-containing compound to thealkali side, and (4) a step of applying ultrasonic wave to the solutionin the air or inert atmosphere. This process produces oxygen electrodecatalyst for fuel cell where catalyst that is represented by the generalformula PtP is supported on the carbon support.

FIG. 1 is a schematic sectional view of the Pt—Ru—P catalyst particulate1 of this invention obtained by the above alcohol reduction method. TheP particle 7 is coordinated on the outer surface of the Pt—Ru particle 5deposited on the carbon support 3. X-ray photoelectron spectroscopyshows that the P particle 7 exists as an oxide. It is assumed that thecoordination of P particle 7 on the outer surface of the Pt—Ru particle5 stops the growth of the Pt—Ru particle 5, thereby minimizing theoverall size of the Pt—Ru—P catalyst particulate 1. (The presentinvention is not limited by this assumption however.)

FIG. 2 is a schematic sectional view of the Pt—Ru—P catalyst particulate1 of this invention obtained by the above electroless plating method.The P particle 7 is coordinated on the outer surface of the Pt—Ruparticle 5 deposited on the carbon support 3. At the same time, Pparticles 8 are incorporated into Pt—Ru particle 5, producing metalphosphide which is suggested by X-ray photoelectron spectroscopy. It isassumed that the coordination of P particle 7 on the outer surface ofthe Pt—Ru particle 5 and incorporation of P particles 8 into Pt—Ruparticle 5 stop the growth of the Pt—Ru particle 5, thereby minimizingthe overall size of the Pt—Ru—P catalyst particulate 1. (The presentinvention is not limited by this assumption however.)

The size of the Pt—P or Pt—Ru—P catalyst particulate generated by themethod of this invention is smaller than that of a conventional Pt orPt—Ru catalyst particulate due to the presence of P. Though the particlesize of Pt or Pt—Ru catalyst generated by a conventional productionprocess is generally about 5 to 10 nm, the particle size of the Pt orPt—Ru catalyst to which P is added according to the present invention issignificantly decreased to 1 to 3 nm. The decrease in the particle sizeincreases the surface area of the Pt—Ru catalyst, which significantlyenhances hydrogen oxidation or methanol oxidation. Another advantage ofthe Pt—P or Pt—Ru—P catalyst particulate of the present invention isthat the distribution range of the particle size is narrower than thatof the conventional Pt or Pt—Ru catalyst particulates. The center of theparticle size distribution range of the Pt or Pt—Ru catalyst produced bythe conventional process is more than 5 nm, and further miniaturizationof the particle has been difficult. The present invention overcomes thisproblem by adding P to the Pt or Pt—Ru catalyst to create the Pt—Pbinary or Pt—Ru—P ternary catalyst.

By adjusting the pH value of an alcohol solvent or water where acompound of platinum, optionally ruthenium, and phosphorus is dissolvedto fall in appropriate value, the composition of the Pt and, if present,Ru on the Pt—P or Pt—Ru—P particulate surface is optimized. This allowsthe oxidation reaction of CO shown by the reaction formula (3) toproceed effectively to enhance the methanol oxidation activity.

An acid used for adjusting the pH value to acidic region is preferablyan acid having a boiling point of 200° C. and above. This is because theheat refluxing of alcohol is performed at about 200° C. in some cases.The acid having the boiling point of less than 200° C. can be evaporatedby the alcohol refluxing, making it difficult to maintain the pH valuewithin a given range. Hence, hydrochloric acid and nitric acid, forexample, are not suitable since they have a low boiling point and thus,are evaporated during the heat refluxing. A sulfuric acid having theboiling point of 290° C. is preferred for use in this invention.

Abase used for adjusting the pH value to basic region is preferablysodium hydroxide or potassium hydroxide for the same reason describedabove.

The P-containing compound available in the production process of thePt—P or Pt—Ru—P catalyst particulate of the present invention includesphosphonic acid and phosphinic acid and derivatives of phosphonic acidand phosphinic acid, such as sodium phosphinate, ammonium phosphinate,disodium hydrogenphosphite, sodium dihydrogenphosphite. Since thepentavalent P-atom has the same electron configuration as Ne, it ischemically stable by the Octet Rule, which is not suitable for thisinvention. Thus, phosphoric acid having the pentavalent P-atom (H₃PO₄)is preferably not be used in this invention. The addition amount of theP-containing compound is preferably within the range of 5to 50% of thetotal moles of Pt and, if present, Ru. If it is less than 5%, the effectof reducing the Pt or Pt—Ru catalyst particle size is not enough, and ifit is more than 50%, the characteristics of the catalyst deteriorate.The P-containing compound may be used independently or in combination.

The Pt salt or complex used in this invention is, for example, platinumacetate, platinum nitrate, platinum dinitrodiamine complex,ethylenediamine platinum complex, triphenylphosphine platinum complex,platinum ammine complex, bis(acetylacetonato)platinum(II), hydrogenhexachloroplatinate. The platinum compound may be used independently orin combination.

The Ru salt or complex used in this invention is, for example, ruthenium(III)chloride n-hydrate, ruthenium acetate, ruthenium nitrate, rutheniumtriphenylphosphine complex, ruthenium ammine complex, rutheniumethylene-diamine complex, tris(acetylacetonato)ruthenium (III). Theruthenium compound may be used independently or in combination.

In alcohol reduction, when compound for catalyst synthesis is dissolvedinto alcohol solution and reduced at a temperature close to a boilingpoint of the alcohol solution, alcohol (R—OH) discharges electronsduring heat refluxing to reduce Pt ion. The alcohol itself is oxidizedinto aldehyde (R—CHO). In electroless plating, when hypophosphite ion isoxidized into phosphorous ion or phosphate ion for example, itdischarges electrons and Pt ion receives the electron and is reduced tometal. In ultrasonic reduction, cavitation creates a high pressure andhigh temperature field to generate reducing chemical species, whichreduces Pt ion.

The alcohol that may be used in the heat refluxing process of thepresent invention includes methyl alcohol, ethyl alcohol, ethyleneglycol, glycerol, propylene glycol, isoamyl alcohol, n-amyl alcohol,sec-butyl alcohol, n-butyl alcohol, isobutyl alcohol, allylalcohol,n-propyl alcohol, 2-ethoxyalcohol, 1,2-hexadecanediol. One type or twoor more types of alcohol may be selected to use. In order to preventoxidation of particulates during reflux, it is preferred to performreflux while displacing the gas in the reaction system with inert gassuch as nitrogen and argon.

A heat temperature and a reflux time in the alcohol reduction processvary by the kind of alcohol in use. Generally, the heat temperature isabout 60° C. to 300° C., and the reflux time is about 30 minutes to 6hours. In the electroless plating process, a general bath temperature isabout 50° C. to 90° C., and a plating time is about 30 minutes to 2hours. In the ultrasonic reduction process, an ultrasonic waveapplication time is about 30 minutes to 4 hours.

In the present invention, the alcohol reduction process dissolves Ptsalt or complex and P-containing compound into at least one kind ofalcohol. The alcohol may or may not contain water. The electrolessplating process and the ultrasonic reduction process dissolve Pt salt orcomplex and P-containing compound into pure water basically. Theelectroless plating process and the ultrasonic reduction process may addthe above-described alcohol as reduction assistant.

The present invention dissolves the Pt and, if present, Ru salt orcomplex and the P-containing compound into an organic solvent composedof at least one type of alcohol. The alcohol may or may not containwater.

A loading rate of the catalyst used in this invention is suitably 30wt %or above. If it is less than 30 wt %, formation of a given amount ofcatalyst results in an increase in the thickness of a catalystelectrode. This increases diffusive resistance of oxygen fuel orgenerated water, which is not suitable. An upper limit of a loading rateis not specified. For example, in order to obtain a loading rate of 80wt%, a specific surface area of a support needs to be 200m²/g or larger ifa catalyst particle diameter is 2 nm. Obtaining catalyst with a highloading rate requires use of a porous carbon support. In such a case aswell, it is needed to use a porous carbon support with the smallestpossible number of fine pores. For example, Vulcan®-XC-72R with aspecific surface of 254 m²/g available from Cabot corporation Inc. maybe used.

The loading rate of the catalyst used in this invention is preferably 50to 70 wt %. If it is less than 50 wt %, the thickness of the catalystelectrode layer is too large and the diffusibility of the fuel decreasesto deteriorate the cell characteristics. On the other hand, if it ismore than 70 wt %, it is too difficult to load the catalyst particles onthe carbon support while supporting the whole catalyst.

Though fuel electrode catalyst to be used in pair with the PtP oxygenelectrode catalyst of the present invention may be the one that is usedconventionally in direct methanol fuel cells and polymer electrolytefuel cells, such as PtRu, it is preferred to use a PtRuP catalystparticle that is described in Japanese Patent Application No.2003-433758, 2004-206232, 2004-271034 and 2004-373450, which arepresented by the inventors of the present invention. As described inthese, the inventors have already found that adding P reduces a particlediameter of PtRu catalyst. By adding P, the PtRu catalyst particlediameter is reduced to less than about 5 nm, preferably 1 to 3 nm, andmore preferably about 2 nm. This increases the specific surface area ofPtRuP catalyst, thereby enhancing the oxidation activity of methanol orhydrogen. Even when non-porous multiwalled carbon nanotube or acetyleneblack is used as a carbon support, the particle diameter of the PtRuPcatalyst is kept to less than 5 nm. Thus, using the PtP oxygen electrodecatalyst in combination with the PtRuP fuel electrode catalyst allowsproducing a fuel cell with significantly high cell characteristics.

EXAMPLE 1

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium phosphinateof 0.338 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a carbon support of 0.5 g (VulcanXC-72R available from E-TEK Inc., Somerset, N.J., with the specificsurface area of 254 m²/g) was dispersed was added thereto. A sulfuricacid solution was added, and the pH value of the solution was adjustedto 3 using a pH litmus paper. In a nitrogen gas atmosphere, the solutionwas stirred and refluxed for 4 hours at 200° C., thereby depositingPt—Ru—P catalyst particulates on the carbon support. Subsequentfiltration, washing, and drying gave a catalyst.

EXAMPLE 2

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodiumdihydrogenphosphite of 0.338 mmol were dissolved into ethylene glycol of300 ml. An ethylene glycol solution of 100 ml into which a carbonsupport of 0.5 g (Vulcan XC-72R with the specific surface area of 254m²/g) was dispersed was added thereto. A sulfuric acid solution wasadded, and the pH value of the solution was adjusted to 3 using a pHlitmus paper. In a nitrogen gas atmosphere, the solution was stirred andrefluxed for 4 hours at 200° C., thereby depositing Pt—Ru—P catalystparticulates on the carbon support. Subsequent filtration, washing, anddrying gave a catalyst.

COMPARATIVE EXAMPLE 1

Bis(acetylacetonato)platinum(II) of 1.69 mmol andtris(acetylacetonato)ruthenium(III) of 1.69 mmol were dissolved intoethylene glycol of 300 ml. An ethylene glycol solution of 100 ml intowhich a carbon support of 0.5 g (Vulcan XC-72R with the specific surfacearea of 254 m²/g) was dispersed was added thereto. A sulfuric acidsolution was added, and the pH value of the solution was adjusted to 3using a pH litmus paper. In a nitrogen gas atmosphere, the solution wasstirred and refluxed for 4 hours at 200° C., thereby depositing Pt—Rucatalyst particulates on the carbon support. Subsequent filtration,washing, and drying gave a catalyst.

COMPARATIVE EXAMPLE 2

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and ammonium molybdateof 0.338 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a carbon support of 0.5 g (VulcanXC-72R with the specific surface area of 254 m²/g) was dispersed wasadded thereto. A sulfuric acid solution was added, and the pH value ofthe solution was adjusted to 3 using a pH litmus paper. In a nitrogengas atmosphere, the solution was stirred and refluxed for 4 hours at200° C., thereby depositing Pt—Ru—Mo catalyst particulates on the carbonsupport. Subsequent filtration, washing, and drying gave a catalyst.

COMPARATIVE EXAMPLE 3

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium tungstateof 0.338 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a carbon support of 0.5 g (VulcanXC-72R with the specific surface area of 254 m²/g) was dispersed wasadded thereto. A sulfuric acid solution was added, and the pH value ofthe solution was adjusted to 3 using a pH litmus paper. In a nitrogengas atmosphere, the solution was stirred and refluxed for 4 hours at200° C., thereby depositing Pt—Ru—W catalyst particulates on the carbonsupport. Subsequent filtration, washing, and drying gave a catalyst.

COMPARATIVE EXAMPLE 4

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, andtris(acetylacetonato)iron(III) of 0.338 mmol were dissolved intoethylene glycol of 300 ml. An ethylene glycol solution of 100 ml intowhich a carbon support of 0.5 g (Vulcan XC-72R with the specific surfacearea of 254 m²/g) was dispersed was added thereto. A sulfuric acidsolution was added, and the pH value of the solution was adjusted to 3using a pH litmus paper. In a nitrogen gas atmosphere, the solution wasstirred and refluxed for 4 hours at 200° C., thereby depositing Pt—Ru—Fecatalyst particulates on the carbon support. Subsequent filtration,washing, and drying gave a catalyst.

COMPARATIVE EXAMPLE 5

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)rutheniu(III) of 1.69 mmol, and Bis(acetylacetonato)cobalt(II) of 0.338 mmol were dissolved into ethyleneglycol of 300 ml. An ethylene glycol solution of 100 ml into which acarbon support of 0.5 g (Vulcan XC-72R with the specific surface area of254 m²/g) was dispersed was added thereto. A sulfuric acid solution wasdropped, and the pH value of the solution was adjusted to 3 using a pHlitmus paper. In a nitrogen gas atmosphere, the solution was stirred andrefluxed for 4 hours at 200° C., thereby depositing Pt—Ru—Co catalystparticulates on the carbon support. Subsequent filtration, washing, anddrying gave a catalyst.

The particle sizes of the catalysts obtained in the above inventiveexamples 1 and 2, and the comparative examples 1 to 5 were observed withan electron microscope. Table 1 below shows the observation result.Though the particle sizes of the catalysts obtained in the comparativeexamples 1 to 5 range to 10 nm, the particle sizes of the Pt—Ru—Pcatalysts obtained in the inventive examples 1 and 2 fall within therange of 1 to 3 nm. TABLE 1 Particle size Sample Catalyst (nm) Example 1Pt—Ru—P 1-3 Example 2 Pt—Ru—P 1-3 Comparative example 1 Pt—Ru ≦10Comparative example 2 Pt—Ru—Mo ≦10 Comparative example 3 Pt—Ru—W ≦10Comparative example 4 Pt—Ru—Fe ≦10 Comparative example 5 Pt—Ru—Co ≦10

The surface of the Pt—Ru—P particulate catalyst on a carbon supportobtained in inventive example 1 and the Pt—Ru particulate catalyst on acarbon support obtained in the comparative example 1 were observed witha transmission electron microscope. The observation results are shown inFIGS. 3A and 3B. FIG. 3A shows an electron microscopic image of thePt—Ru—P particulate catalyst on the carbon support of the example 1, andFIG. 3B shows the Pt—Ru particulate catalyst on the carbon support ofthe comparative example 1. In these images, black to gray black portionsare the catalyst particulates, and light gray to ash gray portions arethe carbon supports. As is obvious from the picture of FIG. 3A, thePt—Ru—P catalyst particulates of this invention have the size of about 1to 3 nm, and the particulates are well dispersed and almost no clusterexists. On the other hand, the Pt—Ru catalyst particulates of thecomparative example 1 include the particulate size of as large as 10 nmand some particulate clusters exist, as in FIG. 3B.

Then, 30 mg of each of the catalysts obtained in the above inventiveexamples 1 and 2, and the comparative examples 1 to 5 was dispersed intoH₂SO₄ with the methanol concentration of 25 vol % and electrolyte of 1.5mol/l and swept between the potential values of 0.2 to 0.6 V vs. normalhydrogen electrode (NHE) at a sweep rate of 0.01V/sec, using a Au linefor a working electrode at 25° C., thereby measuring methanol oxidationactivity. The methanol oxidation current at the potential of 0.6 V vs.NHE is shown in Table 2 below. Table 2 shows that a larger methanoloxidation current was obtained in the Pt—Ru—P catalysts obtained in theinventive examples 1 and 2 than in the catalysts obtained in thecomparative examples 1 to 5, which indicates improvement in the methanoloxidation activity. TABLE 2 Methanol oxidation current (mA at 0.6 V vs.Sample Catalyst NHE) Example 1 Pt—Ru—P 13 Example 2 Pt—Ru—P 13Comparative example 1 Pt—Ru 7 Comparative example 2 Pt—Ru—Mo 7Comparative example 3 Pt—Ru—W 7 Comparative example 4 Pt—Ru—Fe 5Comparative example 5 Pt—Ru—Co 5

The composition of the Pt—Ru—P obtained in the inventive examples 1 and2 was analyzed with X-ray fluorescence. The result was Pt₅₇Ru₃₇P₆ in theinventive example 1 and Pt₅₇Ru₃₈P₅ in the inventive example 2.

EXAMPLE 3

An alcohol solution of pure water and NAFION® dispersion solution,available from E.I. DuPont de Nemours and Company, Wilmington, Del., wasadded to the Pt—Ru—P catalyst deposited on the Vulcan XC-72R obtained ininventive example 1 and stirred, and then its viscosity was adjusted tocreate a catalyst ink. The catalyst ink was then applied onto TEFLON®sheet, available also from Dupont, in such a way that the amount of thePt—Ru—P catalyst is 5 mg/cm². After being dried, the TEFLON® sheet waspeeled off, thereby creating a methanol electrode catalyst. Further, analcohol solution of pure water and NAFION® dispersion solution was addedto the Pt catalyst deposited on Ketjen EC, available from Ketjen BlackInternational. Co., Tokyo, Japan, and stirred, and then its viscositywas adjusted to create a catalyst ink. The catalyst ink was then appliedonto TEFLON® sheet in such a way that the amount of the Pt catalyst is 5mg/cm². After being dried, the TEFLON® sheet was peeled off, therebycreating an oxygen electrode catalyst. Then, the Pt—Ru—P electrodecatalyst and the Pt electrode catalyst were hot pressed to both sides ofa polymer electrolyte membrane (NAFION® membrane, available fromDupont), thereby producing a membrane electrode assembly. Using themethanol electrode, polymer electrolyte membrane, oxygen electrode, anda methanol solution of 15 wt % as a liquid fuel, a direct methanol fuelcell was produced.

The direct methanol fuel cell 10 of FIG. 4 includes an oxygen electrodeside charge collector 12, an oxygen electrode side diffusion layer 14, apolymer electrolyte membrane 16, a methanol electrode side diffusionlayer 18, a methanol electrode side charge collector 20, a methanol fueltank 22, an air intake opening 24, an oxygen electrode (Pt) catalystlayer 26, a methanol electrode (Pt—Ru—P) catalyst layer 28, and amethanol fuel intake opening 30.

The oxygen electrode side charge collector 12 serves as a structure totake in the air (oxygen) through the air intake opening 24 and also as apower collector. The polymer electrolyte membrane 16 (NAFION® membrane,available from DuPont) serves as a carrier for carrying protonsgenerated in the methanol electrode to the oxygen electrode, and also asa separator for preventing the short-circuit of the methanol electrodeand the oxygen electrode. In the direct methanol fuel cell 10 thuscomposed, the liquid fuel supplied from the methanol electrode sidecharge collector 20 passes through the methanol electrode side diffusionlayer 18 and enters the methanol electrode catalyst layer 28 where it isoxidized into CO₂, an electron, and a proton. The proton passes throughthe polymer electrolyte membrane 16 and moves to the oxygen electrodeside. In the oxygen electrode, the oxygen entering from the oxygenelectrode side charge collector 12 is reduced by the electron generatedin the methanol electrode, and this oxygen and the proton react togenerate water. The direct methanol fuel cell 10 of FIG. 4 generateselectric power by the methanol oxidation reaction and the oxygenreduction reaction.

COMPARATIVE EXAMPLE 6

The comparative example 6 produced the direct methanol fuel cell in thesame manner as the example 3 except that it used Pt—Ru catalyst, insteadof the Pt—Ru—P catalyst, for the methanol electrode catalyst.

COMPARATIVE EXAMPLE 7

The comparative example 7 produced the direct methanol fuel cell in thesame manner as the inventive example 3 except that it used Pt—Ru—Mocatalyst, instead of the Pt—Ru—P catalyst, for the methanol electrodecatalyst.

COMPARATIVE EXAMPLE 8

The comparative example 8 produced the direct methanol fuel cell in thesame manner as the inventive example 3 except that it used Pt—Ru—Wcatalyst, instead of the Pt—Ru—P catalyst, for the methanol electrodecatalyst.

COMPARATIVE EXAMPLE 9

The comparative example 9 produced the direct methanol fuel cell in thesame manner as the example 3 except that it used Pt—Ru—Fe catalyst,instead of the Pt—Ru—P catalyst, for the methanol electrode catalyst.

COMPARATIVE EXAMPLE 10

The comparative example 10 produced the direct methanol fuel cell in thesame manner as the inventive example 3 except that it used Pt—Ru—Cocatalyst, instead of the Pt—Ru—P catalyst, for the methanol electrodecatalyst.

The measurement result of the power density of each of the directmethanol fuel cells obtained in the inventive example 3 and thecomparative examples 6 to 10 is shown in Table 3 below. The directmethanol fuel cell of the inventive example 3 using the Pt—Ru—P catalystas the methanol electrode catalyst has the power density of 50 mW/cm².The direct methanol fuel cells of the comparative examples 6 to 10 usinga catalyst different from the Pt—Ru—P catalyst as the methanol electrodecatalyst have the power density of 40 mW/cm² or less. This result showsthat use of the Pt—Ru—P catalyst with the particulate size of 1 to 3 nmas the methanol electrode catalyst allows improving the cellcharacteristics. TABLE 3 Power density Sample Catalyst (mW/cm²) Example3 Pt—Ru—P 50 Comparative example 6 Pt—Ru 40 Comparative example 7Pt—Ru—Mo 40 Comparative example 8 Pt—Ru—W 40 Comparative example 9Pt—Ru—Fe 35 Comparative example 10 Pt—Ru—Co 36

EXAMPLE 4

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium phosphinate(NaPH_(2O) ₂) of 5 to 100 mol % of the total moles of Pt and Ru weredissolved into ethylene glycol of 300 ml. An ethylene glycol solution of100 ml into which a carbon support of 0.5 g (Vulcan XC-72R, specificsurface area of 254 m²/g) was dispersed was added thereto. A sulfuricacid solution was added into this solution and the pH value of thesolution was adjusted to 3 using a pH litmus paper. In a nitrogen gasatmosphere, the solution was stirred and refluxed in an oil bath at 200°C., thereby depositing Pt—Ru—P catalyst particulates on the carbonsupport. Subsequent filtration, washing, and drying gave catalyst.

The X-ray diffraction analysis was performed on the Pt—Ru—P catalystobtained in the inventive example 4, and the particulate size of thePt—Ru—P catalyst was determined by the Scherrer's equation. Then, thecomposition of the catalyst was analyzed by X-ray fluorescence (XRF) andX-ray photoelectron spectroscopy analysis (XPS). Since each analysisshowed that P was likely to exist on the surface of the Pt—Ru catalyst,the XPS which can measure the composition closer to the catalyst surfacewas used for the measurement of the P concentration. Further, themethanol oxidation characteristics of the Pt—Ru—P catalyst weremeasured. The measurement process is as follows. A 30 mg of catalyst wasdispersed into H₂SO₄ with the methanol concentration of 25 vol % andelectrolyte of 1.5 mol/l and swept between the potential values of 0.2to 0.6 V vs. NHE at a sweep rate of 0.01V/sec, using an Au line for aworking electrode at 25° C. The measurement result is shown in Table 4below. It shows that adding 5 to 50 mol % of the sodium phosphinate ofthe total moles of Pt—Ru allows producing a high methanol oxidationcurrent. If, however, 70 mol % or higher sodium phosphinate of the totalmoles of Pt—Ru was added, too much sodium phosphinate inhibited thePt—Ru particulate formation and caused the eduction of thebis-(acetylacetonato)platinum(II), resulted in significant decrease inthe methanol oxidation activity. TABLE 4 Methanol NaPH₂O₂ oxidationadditive Particle Pt—Ru P current rate size Composition Composition (mAat 0.6 V vs. (mol %) (nm) (at. % by XRF) (at. % by XPS) NHE) 5 1.8Pt₆₀—Ru₄₀ 3 11 10 1.6 Pt₆₀—Ru₄₀ 10 13 20 1.6 Pt₆₁—Ru₃₉ 16 16 50 1.3Pt₆₉—Ru₃₁ 27 25 70 1.2 Pt₆₁—Ru₃₉ 55 3 100 1.4 Pt₇₀—Ru₃₀ 65 3

EXAMPLE 5

Bis(acetylacetonato)platinum(II) and tris(acetyl-acetonato)ruthenium(III), the ratio of which was 1:2 to 2:1, and sodium phosphinate of 50mol % of the total moles of Pt—Ru were dissolved into ethylene glycol of300 ml. An ethylene glycol solution of 100 ml where a carbon support of0.5 g (Vulcan XC-72R with the specific surface area of 254 m²/g) wasdispersed was added thereto. A sulfuric acid solution was droppedthereto, and its pH value was adjusted to 3 using a pH litmus paper. Ina nitrogen gas atmosphere, the solution was stirred and refluxed in anoil bath at 200° C., thereby depositing Pt—Ru—P catalyst particulates onthe carbon support. Subsequent filtration, washing, and drying gave acatalyst.

The X-ray diffraction analysis was performed on the Pt—Ru—P catalystobtained in the inventive example 5, and the particulate size of thePt—Ru—P catalyst was determined by the Scherrer's equation. Then, thecomposition of the catalyst was analyzed with the X-ray fluorescence.Further, the methanol oxidation characteristics of the Pt—Ru—P catalystwere measured. The measurement process is as follows. A 30 mg ofcatalyst was dispersed into H₂SO₄ with the methanol concentration of 25vol % and electrolyte of 1.5 mol/l and swept between the potentialvalues of 0.2 to 0.6 V vs. NHE at a sweep rate of 0.01V/sec, using an Auline for a working electrode at 25° C. The measurement result is shownin Table 5 below. TABLE 5 Methanol oxidation Ratio Catalyst current ofPt Particle Composition (mA at 0.6 V and Ru size (nm) (at. %) vs. NHE)1:2 1.7 Pt₄₆—Ru₄₈—P₆ 9   1:1.5 1.7 Pt₅₃—Ru₃₇—P₁₀ 11 1:1 1.3 Pt₆₅—Ru₂₉—P₆25 1.5:1   1.5 Pt₇₃—Ru₂₁—P₆ 34 2:1 1.7 Pt₈₀—Ru₁₄—P₆ 27

The measurement result of Table 5 shows that setting the ratio of Pt andRu to 1:2 to 2:1 allows producing the Pt—Ru—P catalyst where the Ptcomposition is 40 to 90 at. % and the P is 5 at. % or higher, therebycreating a high methanol oxidation current.

EXAMPLE 6

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium phosphinateof 0.338 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a carbon support of 0.5 g (Vulcan Pwith the specific surface area of 140 m²/g) was dispersed was addedthereto. A sulfuric acid solution was added into this solution, and thepH value of the solution was adjusted to 3 using a pH litmus paper. In anitrogen gas atmosphere, the solution was stirred and refluxed in an oilbath at 200° C. for 4 hours, thereby depositing Pt—Ru—P catalystparticulates on the carbon support. Subsequent filtration, washing, anddrying gave a catalyst.

The sizes of catalyst particulates obtained in the inventive example 6was observed with an electron microscope. Table 6 below shows theobservation result. The particulate sizes of the Pt—Ru—P catalyst werein the range of 1 to 3 nm in the inventive example 6. TABLE 6 CatalystParticle size Catalyst (nm) Example 6 Pt—Ru—P 1-3

The methanol oxidation activity of the catalyst obtained in theinventive example 6 was observed. The measurement process is as follows.A 30 mg of each catalyst was dispersed into H₂SO₄ with the methanolconcentration of 25 vol % and electrolyte of 1.5 mol/l and swept betweenthe potential values of 0.2 to 0.6 V vs. NHE at a sweep rate of0.01V/sec, using an Au line for a working electrode at 25° C. Themethanol oxidation activity was thus measured. The current density atthe potential 0.6 V vs. NHE was shown in Table 7 below. Table 7 showsthe result of the inventive example 1, too. The inventive examples 6 and1 where the specific surfaces of the carbon supports were 140 m²/g and254 m²/g, respectively, created a high methanol oxidation current.

Further, in the case of using Vulcan P with the specific surface of the140 m²/g, the methanol oxidation current was higher than the case ofusing Vulcan XC-72R with the specific surface of the 254 m²/g. This isbecause the Vulcan P with the small specific surface had a smallernumber of pores with a larger diameter, and thereby the number ofparticulates of the Pt—Ru—P catalyst creating three-phase interfaces(catalyst/methanol/acid) increased. TABLE 7 Methanol Support oxidationspecific current surface (mA at 0.6 V Catalyst (m²/g) vs. NHE) Example 6Pt—Ru—P 140 19 Example 1 Pt—Ru—P 254 13

EXAMPLE 7

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium phosphinateof 1.69 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a carbon support of 0.5 g (VulcanXC-72R with the specific surface area of 254 m²/g) was dispersed wasadded thereto. A sulfuric acid solution was added into this solution,and the pH value of the solution was adjusted to 3 using a pH litmuspaper. In a nitrogen gas atmosphere, the solution was stirred andrefluxed in an oil bath at 200° C. for 4 hours, thereby depositingPt—Ru—P catalyst particulates on the carbon support. Subsequentfiltration, washing, and drying gave a catalyst. The observation of thesize of the obtained Pt—Ru—P catalyst with the electron microscopeshowed 1 to 3 nm. The analysis of the composition with X-rayfluorescence showed Pt₆₅Ru₂₉P₆.

EXAMPLE 8

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium phosphinateof 1.69 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a carbon support of 0.5 g (Vulcan Pwith the specific surface area of 140 m²/g) was dispersed was addedthereto. A sulfuric acid solution was added into this solution, and thepH value of the solution was adjusted to 3 using a pH litmus paper. In anitrogen gas atmosphere, the solution was stirred and refluxed in an oilbath at 200° C. for 4 hours, thereby depositing Pt—Ru—P catalystparticulates on the carbon support. Subsequent filtration, washing, anddrying gave a catalyst. The observation of the size of the obtainedPt—Ru—P catalyst with the electron microscope showed 1 to 3 nm. Theanalysis of the composition with X-ray fluorescence showed Pt₆₅Ru₂₉P₆.

EXAMPLE 9, 10 AND COMPARATIVE EXAMPLE 11

An alcohol solution of pure water and NAFION® dispersion solution,available from DuPont, was added to each of the Pt—Ru—P catalystsobtained in the examples 7 and 8 and stirred, and then its viscosity wasadjusted to create a catalyst ink. The catalyst ink was then appliedonto TEFLON® sheet, available also from Dupont, in such a way that theamount of the Pt—Ru—P catalyst is 5 mg/cm². After being dried, theTEFLON® sheet was peeled off, thereby creating a methanol electrodecatalyst. Further, an alcohol solution of pure water and NAFION®dispersion solution was added to the Pt catalyst deposited on Ketjen ECand stirred, and then its viscosity was adjusted to create a catalystink. The catalyst ink was then applied onto TEFLON® sheet in such a waythat the amount of the Pt catalyst was 5 mg/cm². After dried, theTEFLON® sheet was peeled off, thereby creating an oxygen electrodecatalyst. Then, the Pt—Ru—P electrode catalyst and the Pt electrodecatalyst were hot pressed to both sides of a polymer electrolytemembrane (NAFION® membrane, available also from Dupont), therebyproducing a membrane electrode assembly. Using the methanol electrode,polymer electrolyte membrane, oxygen electrode, and a methanol solutionof 15 wt % as a liquid fuel, a direct methanol fuel cell shown in FIG. 4was produced. Table 8 below shows the observation result of the powerdensity characteristics of the direct methanol fuel cell. Table 8includes the power density characteristics in the comparative example 11where the Pt—Ru catalyst is used as a methanol electrode catalyst. Inthe case of using the Vulcan P support with the specific surface area of140 m²/g, the power density was 65 mW/cm². In the case of using theVulcan XC-72R support with the specific surface area of 254 m²/g, on theother hand, the power density was 59 mW/cm². As described above, sincethe Vulcan P support with the smaller specific surface had a smallernumber of pores with a larger diameter than the Vulcan XC-72R support,the Pt—Ru—P catalyst particulates were not likely to be buried into thepores to cease to function as a catalyst, thereby increasing the numberof particulates of the Pt—Ru—P catalyst creating three-phase interfaces(catalyst/electlyte/methanol). TABLE 8 NaPH₂O₂ Support additive specificPower Ratio of rate surface density Electrode catalyst pH Pt and Ru (mol%) (m²/g) (mW/cm²) Example 9 3 1:1 50 254 59 Example 10 3 1:1 50 140 65Comparative example 3 1:1 — 254 40 11

EXAMPLE 11 AND 12

An alcohol solution of pure water and NAFION® dispersion solution,available from DuPont, was added to each of the Pt—Ru—P catalystsobtained in the inventive examples 7 and 8 and stirred, and then itsviscosity was adjusted to create a catalyst ink. The catalyst ink wasthen applied onto TEFLON® sheet, available also from Dupont, in such away that the amount of the Pt—Ru—P catalyst was 5 mg/cm². After beingdried, the TEFLON® sheet was peeled off, thereby creating a hydrogenelectrode catalyst. Further, an alcohol solution of pure water andNAFION® dispersion solution was added to Pt catalyst deposited on aKetjen EC support and stirred, and its viscosity was adjusted to createa catalyst ink. The catalyst ink was then applied onto TEFLON® sheet insuch a way that the amount of the Pt catalyst was 5 mg/cm². After beingdried, the TEFLON® sheet was peeled off, thereby creating an oxygenelectrode catalyst. Then, the Pt—Ru—P electrode catalyst and the Ptelectrode catalyst were hot pressed to both sides of a polymerelectrolyte membrane (NAFION® membrane), thereby producing a membraneelectrode assembly. Using the hydrogen electrode, polymer electrolytemembrane, oxygen electrode, and a hydrogen gas as a fuel, a polymerelectrolyte fuel cell shown in FIG. 5 was produced.

The polymer electrolyte fuel cell 40 of FIG. 5 includes an oxygenelectrode side charge collector 44, an oxygen electrode side diffusionlayer 43, a polymer electrolyte membrane 41, a methanol electrode sidediffusion layer 48, a hydrogen electrode side charge collector 47, anair intake opening 42, an oxygen electrode (Pt) catalyst layer 45, ahydrogen electrode (Pt—Ru—P) catalyst layer 46, and a hydrogen fuelintake opening 49.

The oxygen electrode side charge collector 44 serves as a structure totake in the air (oxygen) through the air intake opening 42 and also as apower collector. The polymer electrolyte membrane 41 (NAFION® membrane)serves as a carrier for carrying proton generated in the hydrogenelectrode to the oxygen electrode side, and also as a separator forpreventing the short-circuit of the hydrogen electrode and the oxygenelectrode. In the polymer electrolyte fuel cell 40 thus composed, thehydrogen gas supplied from the hydrogen electrode side charge collector47 passes through the hydrogen electrode side diffusion layer 48 andenters the hydrogen electrode catalyst layer 46 where it is oxidizedinto an electron and a proton. The proton passes through the polymerelectrolyte membrane 41 and moves to the oxygen electrode side. In theoxygen electrode, the oxygen entering from the oxygen electrode sidecharge collector 44 is reduced by the electron generated in the hydrogenelectrode, and this oxygen and the proton react to generate water. Thepolymer electrolyte fuel cell 40 of FIG. 5 generates electric power bythe hydrogen oxidation reaction and the oxygen reduction reaction.

COMPARATIVE EXAMPLE 12

For comparative example 12 the polymer electrolyte fuel cell is producedin the same manner as the inventive example 11 and 12 except that itused Pt—Ru catalyst created in the comparative example 1 for thehydrogen electrode catalyst.

The measurement result of the power density of each of the polymerelectrolyte fuel cells obtained in the inventive example 11 and 12 andthe comparative example 12 is shown in the Table 9 below. The polymerelectrolyte fuel cell of the inventive example 11 and 12 uses thePt—Ru—P catalyst with the particulate size of 1 to 3 nm and has a highpower density. In the polymer electrolyte fuel cell as well, use ofVulcan P having a smaller support surface area shows a higher powerdensity. If the support is Vulcan P having a small specific surface, itenhances the Pt—Ru—P catalyst particulates to create three-phaseinterfaces, which increases the number of active catalyst particulatesto make higher power density. On the other hand, the polymer electrolytefuel cell of the comparative example 12 uses the Pt—Ru catalyst with theparticulate size up to 10 nm and thus has a low power density of 120mW/cm². TABLE 9 NaPH₂O₂ Support Ratio of additive specific Power Pt ratesurface density Electrode catalyst pH and Ru (mol %) (m²/g) (mW/cm²)Example 11 (Pt—Ru—P) 3 1:1 50 254 180 Example 12 (Pt—Ru—P) 3 1:1 50 140200 Comparative example 3 1:1 — 254 120 12 (Pt—Ru)

EXAMPLE 13

Bis(acetylacetonato)platinum(II) andtris(acetyl-acetonato)ruthenium(III), the ratio of which was 1.5:1, andsodium phosphinate of 50 mol % of the total moles of Pt—Ru weredissolved into ethylene glycol of 300 ml. An ethylene glycol solution of100 ml into which a carbon support of 0.5 g (Vulcan P with the specificsurface area of 140 m²/g) was dispersed was added thereto. At this time,the used amount of the bis(acetylacetonato)platinum(II) and thetris(acetylacetonato)ruthenium (III) was adjusted so that the loadingrate of the Pt—Ru—P catalyst was 50 wt %. Then, a sulfuric acid solutionwas added thereto, and its pH value was adjusted to 3 using a pH litmuspaper. In a nitrogen gas atmosphere, the solution was stirred andrefluxed in an oil bath at 200° C. for 4 hours, thereby depositingPt—Ru—P catalyst particulates on the carbon support. Subsequentfiltration, washing, and drying gave the Pt—Ru—P catalyst with theloading rate of 50 wt %.

EXAMPLE 14

Bis(acetylacetonato)platinum(II) andtris(acetyl-acetonato)ruthenium(III), the ratio of which was changed to1.5:1, and sodium phosphinate of 50 mol % of the total moles of Pt—Ruwere dissolved into ethylene glycol of 300 ml. An ethylene glycolsolution of 100 ml into which a carbon support of 0.5 g (Vulcan P withthe specific surface area of 140 m²/g) was dispersed was added thereto.At this time, the used amount of the bis(acetyl-acetonato)platinum(II)and the tris(acetylacetonato) ruthenium (III) was adjusted so that theloading rate of the Pt—Ru—P catalyst was 60 wt %. Then, a sulfuric acidsolution was added thereto, and its pH value was adjusted to 3 using apH litmus paper. In a nitrogen gas atmosphere, the solution was stirredand refluxed in an oil bath at 200° C. for 4 hours, thereby depositingPt—Ru—P catalyst particulates on the carbon support. Subsequentfiltration, washing, and drying gave the Pt—Ru—P catalyst with theloading rate of 60 wt %.

The methanol oxidation activity of the catalysts obtained in theinventive examples 13 and 14 was observed. The measurement process is asfollows. A 30 mg of each catalyst was dispersed into H₂SO₄ with themethanol concentration of 25 vol % and electrolyte of 1.5 mol/l andswept between the potential values of 0.2 to 0.6 V vs. NHE at a sweeprate of 0.01V/sec, using an Au line for a working electrode at 25° C.The methanol oxidation activity was thus measured. The methanoloxidation current at the potential 0.6 V vs. NHE is shown in Table 10below. TABLE 10 Ratio Methanol of NaPH₂O₂ Support Catalyst oxidation Ptadditive specific deposition current and rate surface rate (mA at 0.6 pHRu (mol %) (m²/g) (wt. %) V vs. NHE) Example 13 3 1.5:1 50 140 50 28Example 14 3 1.5:1 50 140 60 32

EXAMPLE 15 AND 16

The direct methanol fuel cell shown in FIG. 4 was produced using thePt—Ru—P catalysts obtained in the inventive examples 13 and 14. Sincethe deposition rate of the catalysts was different between the inventiveexamples 13 and 14, the same amount of the catalyst, 5 mg/cm², wasapplied to the electrodes. The measurement result of the power densityis shown in the Table 11 below. When the deposition rate of the Pt—Ru—Pcatalyst was 50 wt %, the power density was 70 mW/cm², and when the ratewas 60 wt %, the power density was 80 mW/cm², showing high powerdensities. This result shows that the higher power density was obtainedwhen the loading rate of the catalyst was higher, which is 60 wt %. Thisis because, even if the catalyst application amount to the electrode wasthe same, 5 mg/cm², the electrode becomes thinner when the loading rateof the catalyst was as high as 60 wt %, which increased the permeabilityof the methanol fuel. TABLE 11 Catalyst application amount on CatalystPower electrode deposition density (mg/cm²) rate (wt. %) (mW/cm²)Example 15 5 50 70 Example 16 5 60 80

EXAMPLE 17 AND 18

The polymer electrolyte fuel cell shown in FIG. 5 was produced using thePt—Ru—P catalyst obtained in the examples 13 and 14. Since the loadingrate of the catalysts was different between the inventive examples 13and 14, the same amount of the catalyst, 5 mg/cm², was applied to theelectrodes. The measurement result of the power density is shown in theTable 12 below. When the deposition rate of the Pt—Ru—P catalyst was 50wt %, the power density was 220 mW/cm², and when the rate was 60 wt %,the power density was 240 mW/cm², showing high power densities. Thisresult shows that the higher power density was obtained when the loadingrate of the catalyst was higher, which is 60 wt %. This is because, evenif the catalyst application amount to the electrode was the same, 5mg/cm², the electrode becomes thinner when the loading rate of thecatalyst was as high as 60 wt %, which increased the permeability of thehydrogen gas fuel. TABLE 12 Catalyst application amount on CatalystPower electrode deposition density (mg/cm²) rate (wt. %) (mW/cm²)Example 17 5 50 220 Example 18 5 60 240

EXAMPLE 19

A carbon support (Vulcan XC-72R with the specific surface of 254 m²/g)of 0.25 g was dispersed into pure water of 60 ml. Then, hydrogenhexachloroplatinate hexahydrate of 0.844 mmol and ruthenium (III)chloride n-hydrate of 0.844 mmol were dissolved into pure water of 60ml, and added thereto. Further, sodium phosphinate monohydrate of 5.908mmol was dissolved into pure water of 70 ml and added thereto. Afterthat, 3 mol/l of sodium hydroxide solution was added into the solutionand the pH value of the solution was adjusted to 11. The solution wasthen stirred for 30 minutes at room temperature; then, the temperatureof the solution was increased to 80° C. After that, electroless platingwas performed for two hours while stirring, thereby depositing thecatalyst particulates on the carbon support. Subsequent filtration,washing, and drying gave a catalyst.

The observation result of the particulate sizes of the catalyst obtainedin the inventive example 19 showed 1 to 3 nm. The analysis result of thecomposition of the catalyst with X-ray fluorescence showed Pt₅₉Ru₃₄P₇.

The methanol oxidation activity of the Pt—Ru—P catalyst obtained in theinventive example 19 was observed. The measurement process is asfollows. A 30 mg of each catalyst was dispersed into H₂SO₄ with themethanol concentration of 25 vol % and electrolyte of 1.5 mol/l andswept between the potential values of 0.2 to 0.6 V vs. NHE at a sweeprate of 0.01V/sec, using an Au line for a working electrode at 25° C.The methanol oxidation activity was thus measured. The methanoloxidation current at the potential of 0.6 V vs. NHE is shown in Table 13below. Table 13 shows the methanol oxidation current of Pt—Ru of thecomparative example 1 as well. In the Pt—Ru—P catalyst of the inventiveexample 19, the particulates sizes were decreased to 1 to 3 nm since Pwas added. This increased the active surface area to create a highermethanol oxidation current than in the comparative example 1. Thisexample shows that the Pt—Ru—P catalyst with the particulate size of 1to 3 nm can be created not only by the alcohol reduction method, butalso by the electroless plating method. The electroless plating methoddoes not use organic solvent such as alcohol and allows for the use ofhydrogen hexachloroplatinate and ruthenium chloride for a supply sourceof Pt and Ru, thus having the advantage of significantly reducingcatalyst costs. TABLE 13 Methanol Catalyst oxidation particle current(mA at Catalyst size (nm) 0.6 V vs. NHE) Example 19 Pt—Ru—P 1-3 37Comparative Pt—Ru ≦10 7 Example 1

EXAMPLE 20

Bis(acetylacetonato)platinum(II) of 1.69 mmol,tris(acetylacetonato)ruthenium(III) of 1.69 mmol, and sodium phosphinateof 1.69 mmol were dissolved into ethylene glycol of 300 ml. An ethyleneglycol solution of 100 ml into which a multi-walled carbon nanotubesupport of 0.5 g (the specific surface area of 30 m²/g) was dispersedwas added thereto. A sulfuric acid solution was added into thissolution, and the pH value of the solution was adjusted to 3 using a pHlitmus paper. In a nitrogen gas atmosphere, the solution was stirred andrefluxed in an oil bath at 200° C. for 4 hours, thereby depositingPt—Ru—P catalyst particulates on the multi-walled carbon nanotubesupport. Subsequent filtration, washing, and drying gave a catalyst. Theobservation of the size of the obtained Pt—Ru—P catalyst with theelectron microscope showed 1 to 3 nm. The analysis of the compositionwith X-ray fluorescence showed Pt₄₂Ru₃₉P₁₉.

EXAMPLE 21

The methanol oxidation activity of the Pt—Ru—P catalyst obtained in theinventive example 20 was observed. The measurement process is asfollows. A 30 mg of the catalyst was dispersed into H₂SO₄ with themethanol concentration of 25 vol % and electrolyte of 1.5 mol/l andswept between the potential values of 0.2 to 0.6 V vs. NHE at a sweeprate of 0.01V/sec, using an Au line for a working electrode at 25’ C.The methanol oxidation activity was thus measured. The methanoloxidation current at the potential of 0.6 V vs. NHE is shown in Table 14below. Table 14 shows the methanol oxidation current of Pt—Ru of thecomparative example 1 as well. In the Pt—Ru—P catalyst of the inventiveexample 20, the particulates sizes were decreased to 1 to 3 nm since Pwas added. This increased the active surface area to create a highermethanol oxidation current than in the comparative example 1. TABLE 14Catalyst Methanol oxidation particle current Catalyst size (nm) (mA at0.6 V vs. NHE) Example 21 Pt—Ru—P 1-3 40 Comparative Pt—Ru ≦10 7 Example1

EXAMPLE 22

The direct methanol fuel cell shown in FIG. 4 was produced using thePt—Ru—P catalysts obtained in the inventive examples 20. The measurementresult of the power density is shown in the Table 15 below. Table 15shows the power density of the inventive examples 9 and of thecomparative example 11 as well. When the carbon support is multi-walledcarbon nanotube, power density of 80 mW/cm² was achieved. This value ishigher than that of inventive examples 9 although the size of thePt—Ru—P catalyst particulates is same in 1 to 3 nm. Carbon black (VulcanXC-72R, specific surface area of 254 m²/g) has pores in which Pt—Ru—Pcatalyst particulates are buried. Multi-walled carbon nanotube, however,has no pores so that all the Pt—Ru—P catalyst particulates can educe onthe surface of multi-walled carbon nanotube. Thereby, the utilizationrate of the Pt—Ru—P catalyst particulates was markedly enhances, whichimproved power density. TABLE 15 NaPH₂O₂ Support Ratio of additivespecific Power Pt rate surface density Electrode catalyst pH and Ru (mol%) (m²/g) (mW/cm²) Example 22 3 1:1 50 30 80 Example 9 3 1:1 50 254 59Comparative example 11 3 1:1 — 254 40

COMPARATIVE EXAMPLE 13

Bis(acetylacetonato)platinum(II) of 1.69 mmol andtris(acetylacetonato)ruthenium(III) of 1.69 mmol were dissolved intoethylene glycol of 300 ml. An ethylene glycol solution of 100 ml intowhich a multi-walled carbon nanotube support of 0.5 g (the specificsurface area of 30 m²/g) was dispersed was added thereto. A sulfuricacid solution was added into this solution, and the pH value of thesolution was adjusted to 3 using a pH litmus paper. In a nitrogen gasatmosphere, the solution was stirred and refluxed in an oil bath at 200°C. for 4 hours, thereby depositing Pt—Ru catalyst particulates on themulti-walled carbon nanotube support. Subsequent filtration, washing,and drying gave a catalyst. The observation of the size of the obtainedPt—Ru catalyst with the electron microscope showed ˜10 nm. The analysisof the composition with X-ray fluorescence showed Pt₅₄RU₄₆.

COMPARATIVE EXAMPLE 14

The methanol oxidation activity of the Pt—Ru catalyst obtained in thecomparative example 13 was observed. The measurement process is asfollows. A 30 mg of the catalyst was dispersed into H₂SO₄ with themethanol concentration of 25 vol % and electrolyte of 1.5 mol/l andswept between the potential values of 0.2 to 0.6 V vs. NHE at a sweeprate of 0.01V/sec, using an Au line for a working electrode at 25° C.The methanol oxidation activity was thus measured. The methanoloxidation current at the potential of 0.6 V vs. NHE was 7 mA. This lowmethanol oxidation current is due to the large size of Pt—Ru catalystparticulates of ˜10 nm because P is not added.

COMPARATIVE EXAMPLE 15

The direct methanol fuel cell shown in FIG. 4 was produced using thePt—Ru catalysts obtained in the comparative examples 13. The measurementresult of the power density was 42 mW/cm². This low power density is dueto the large size of Pt—Ru catalyst particulates of ˜10 nm because P isnot added.

EXAMPLE 23

The Pt—Ru—P catalyst particulates of inventive examples 20 were observedby transmission electron microscope. The observation results are shownin FIGS. 6A and 6B. FIG. 6A shows the Pt—Ru—P catalyst particulates ofinventive examples 20, and FIG. 6B shows the Pt—Ru catalyst particulatesof comparative examples 13. In these images, black to gray blackportions are the catalyst particulates, and light gray to ash grayportions are the carbon supports. As is obvious from the picture of FIG.6A, the Pt—Ru—P catalyst particulates of inventive example 20 have thesize of about 2 to 3 nm, and the particulates are well dispersed and nocluster exists. On the other hand, the Pt—Ru catalyst particulates ofthe comparative example 13 include the particulate size of as large as10 nm and some particulate clusters exist, as in FIG. 6B.

EXAMPLE 24

Bis(acetylacetonato)platinum(II) of 1.69 mmol and sodium hypophosphiteof 0.845 mmol were dissolved into ethylene glycol of 200 ml and added toan ethylene glycol solution of 200 ml that contains dispersedmultiwalled carbon nanotube (MWCNT) with a specific surface area of 30m²/g of 0.5 g as a non-porous support. A sulfuric acid solution wasdropped, and the pH value of the solution was adjusted to 3 by using apH litmus paper. In a nitrogen gas atmosphere, the solution was stirredand refluxed for 4 hours at 200° C. so as to deposit PtP catalyst on themultiwalled carbon nanotube. After the reaction ends, filtration,washing, and drying were performed, thereby producing catalyst.

EXAMPLE 25

Bis(acetylacetonato)platinum(II) of 1.69 mmol and sodium hypophosphiteof 0.845 mmol were dissolved into ethylene glycol of 200 ml and added toan ethylene glycol solution of 200 ml that contains dispersed acetyleneblack (AB) with a specific surface area of 68 m²/g of 0.5 g as anon-porous support. A sulfuric acid solution was dropped, and the pHvalue of the solution was adjusted to 3 by using a pH litmus paper. In anitrogen gas atmosphere, the solution was stirred and refluxed for 4hours at 200° C. so as to deposit PtP catalyst on the acetylene black.After the reaction ends, filtration, washing, and drying were performed,thereby producing catalyst.

EXAMPLE 26

Bis(acetylacetonato)platinum(II) of 1.69 mmol and sodium hypophosphiteof 0.845 mmol were dissolved into ethylene glycol of 200 ml and added toan ethylene glycol solution of 200 ml that contains dispersed carbonblack (CB) with a specific surface area of 140 m²/g of 0.5 g as a poroussupport. A sulfuric acid solution was dropped, and the pH value of thesolution was adjusted to 3 by using a pH litmus paper. In a nitrogen gasatmosphere, the solution was stirred and refluxed for 4 hours at 200° C.so as to deposit PtP catalyst on the carbon black. After the reactionends, filtration, washing, and drying were performed, thereby producingcatalyst.

EXAMPLE 27

Bis(acetylacetonato)platinum(II) of 1.69 mmol and sodium phosphite of0.845 mmol were dissolved into ethylene glycol of 200 ml and added to anethylene glycol solution of 130 ml that contains dispersed multiwalledcarbon nanotube (MWCNT) with a specific surface area of 30 m²/g of 0.5 gas a non-porous support. A sulfuric acid solution was dropped, and thepH value of the solution was adjusted to 3 by using a pH litmus paper.In a nitrogen gas atmosphere, the solution was stirred and refluxed for4 hours at 200° C. so as to deposit PtP catalyst on the multiwalledcarbon nanotube. After the reaction ends, filtration, washing, anddrying were performed, thereby producing catalyst.

EXAMPLE 28

Bis(acetylacetonato)platinum(II) of 1.69 mmol and sodium phosphite of0.845 mmol were dissolved into ethylene glycol of 200 ml and added to anethylene glycol solution of 130 ml that contains dispersed acetyleneblack (AB) with a specific surface area of 68 m²/g of 0.5 g as anon-porous support. A sulfuric acid solution was dropped, and the pHvalue of the solution was adjusted to 3 by using a pH litmus paper. In anitrogen gas atmosphere, the solution was stirred and refluxed for 4hours at 200° C. so as to deposit PtP catalyst on the acetylene black.After the reaction ends, filtration, washing, and drying were performed,thereby producing catalyst.

EXAMPLE 29

Bis(acetylacetonato)platinum(II) of 1.69 mmol and sodium phosphite of0.845 mmol were dissolved into ethylene glycol of 200 ml and added to anethylene glycol solution of 130 ml that contains dispersed carbon black(CB) with a specific surface area of 140 m²/g of 0.5 g as a poroussupport. A sulfuric acid solution was dropped, and the pH value of thesolution was adjusted to 3 by using a pH litmus paper. In a nitrogen gasatmosphere, the solution was stirred and refluxed for 4 hours at 200° C.so as to deposit PtP catalyst on the carbon black. After the reactionends, filtration, washing, and drying were performed, thereby producingcatalyst.

EXAMPLE 30

Multiwalled carbon nanotube (MWCNT), which is a non-porous support, witha specific surface area of 30 m²/g of 0.5 g was dispersed into purewater. Platinic hexachloride of hexahydrate of 1.69 mmol and sodiumhypophosphite of 6.76 mmol were dissolved into pure water of 500 ml andadded. Sodium hydroxide solution was dropped, and the pH value of thesolution was adjusted to 12 by using a pH meter. In the air, thesolution temperature was raised to 80° C. by using a hot plate whilebeing stirred. The electroless plating was performed for 1 hour at thistemperature so as to deposit PtP catalyst on the multiwalled carbonnanotube. After the reaction ends, filtration, washing, and drying wereperformed, thereby producing catalyst.

EXAMPLE 31

Acetylene black (AB), which is a non-porous support, with a specificsurface area of 68 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium hypophosphite of6.76 mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 12 by using a pH meter. In the air, the solution temperaturewas raised to 80° C. by using a hot plate while being stirred. Theelectroless plating was performed for 1 hour at this temperature so asto deposit PtP catalyst on the acetylene black. After the reaction ends,filtration, washing, and drying were performed, thereby producingcatalyst.

EXAMPLE 32

Carbon black (CB), which is a porous support, with a specific surfacearea of 140 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium hypophosphite of6.76 mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 12 by using a pH meter. In the air, the solution temperaturewas raised to 80° C. by using a hot plate while being stirred. Theelectroless plating was performed for 1 hour at this temperature so asto deposit PtP catalyst on the carbon black. After the reaction ends,filtration, washing, and drying were performed, thereby producingcatalyst.

EXAMPLE 33

Multiwalled carbon nanotube (MWCNT), which is a non-porous support, witha specific surface area of 30 m²/g of 0.5 g was dispersed into purewater. Platinic hexachloride of hexahydrate of 1.69 mmol and sodiumphosphite of 6.76 mmol were dissolved into pure water of 500 ml andadded. Sodium hydroxide solution was dropped, and the pH value of thesolution was adjusted to 12 by using a pH meter. In the air, thesolution temperature was raised to 80° C. by using a hot plate whilebeing stirred. The electroless plating was performed for 1 hour at thistemperature so as to deposit PtP catalyst on the multiwalled carbonnanotube. After the reaction ends, filtration, washing, and drying wereperformed, thereby producing catalyst.

EXAMPLE 34

Acetylene black (AB), which is a non-porous support, with a specificsurface area of 68 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium phosphite of 6.76mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 12 by using a pH meter. In the air, the solution temperaturewas raised to 80° C. by using a hot plate while being stirred. Theelectroless plating was performed for 1 hour at this temperature so asto deposit PtP catalyst on the acetylene black. After the reaction ends,filtration, washing, and drying were performed, thereby producingcatalyst.

EXAMPLE 35

Carbon black (CB), which is a porous support, with a specific surfacearea of 140 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium phosphite of 6.76mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 12 by using a pH meter. In the air, the solution temperaturewas raised to 80° C. by using a hot plate while being stirred. Theelectroless plating was performed for 1 hour at this temperature so asto deposit PtP catalyst on the carbon black. After the reaction ends,filtration, washing, and drying were performed, thereby producingcatalyst.

EXAMPLE 36

Multiwalled carbon nanotube (MWCNT), which is a non-porous support, witha specific surface area of 30 m²/g of 0.5 g was dispersed into purewater. Platinic hexachloride of hexahydrate of 1.69 mmol and sodiumhypophosphite of 0.845 mmol were dissolved into pure water of 500 ml andadded. Sodium hydroxide solution was dropped, and the pH value of thesolution was adjusted to 10 by using a pH meter. In the air, ultrasonicwave was applied to the solution for 2 hours by using a commerciallyavailable ultrasonic cleaner so as to deposit PtP catalyst on themultiwalled carbon nanotube. After the reaction ends, filtration,washing, and drying were performed, thereby producing catalyst.

EXAMPLE 37

Acetylene black (AB), which is a non-porous support, with a specificsurface area of 68 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium hypophosphite of0.845 mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 10 by using a pH meter. In the air, ultrasonic wave wasapplied to the solution for 2 hours by using a commercially availableultrasonic cleaner so as to deposit PtP catalyst on the acetylene black.After the reaction ends, filtration, washing, and drying were performed,thereby producing catalyst.

EXAMPLE 38

Carbon black (CB), which is a porous support, with a specific surfacearea of 140 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium hypophosphite of0.845 mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 10 by using a pH meter. In the air, ultrasonic wave isapplied to the solution for 2 hours by using a commercially availableultrasonic cleaner so as to deposit PtP catalyst on the carbon black.After the reaction ends, filtration, washing, and drying were performed,thereby producing catalyst.

EXAMPLE 39

Multiwalled carbon nanotube (MWCNT), which is a non-porous support, witha specific surface area of 30 m²/g of 0.5 g was dispersed into purewater. Platinic hexachloride of hexahydrate of 1.69 mmol and sodiumphosphite of 0.845 mmol were dissolved into pure water of 500 ml andadded. Sodium hydroxide solution was dropped, and the pH value of thesolution was adjusted to 10 using a pH meter. In the air, ultrasonicwave was applied to the solution for 2 hours by using a commerciallyavailable ultrasonic cleaner so as to deposit PtP catalyst on themultiwalled carbon nanotube. After the reaction ends, filtration,washing, and drying were performed, thereby producing catalyst.

EXAMPLE 40

Acetylene black (AB), which is a non-porous support, with a specificsurface area of 68 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium phosphite of 0.845mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 10 using a pH meter. In the air, ultrasonic wave was appliedto the solution for 2 hours by using a commercially available ultrasoniccleaner so as to deposit PtP catalyst on the acetylene black. After thereaction ends, filtration, washing, and drying were performed, therebyproducing catalyst.

EXAMPLE 41

Carbon black (CB), which is a porous support, with a specific surfacearea of 140 m²/g of 0.5 g was dispersed into pure water. Platinichexachloride of hexahydrate of 1.69 mmol and sodium phosphite of 0.845mmol were dissolved into pure water of 500 ml and added. Sodiumhydroxide solution was dropped, and the pH value of the solution wasadjusted to 10 using a pH meter. In the air, ultrasonic wave is appliedto the solution for 2 hours by using a commercially available ultrasoniccleaner so as to deposit PtP catalyst on the carbon black. After thereaction ends, filtration, washing, and drying were performed, therebyproducing catalyst.

EXAMPLE 42

Platinic hexachloride of hexahydrate of 1.69 mmol and sodiumhypophosphite of 0.845 mmol were dissolved into ethylene glycol solutionof 200 ml (ethylene glycol:water=50 vol. %:50 vol. %) and added to anethylene glycol solution of 200 ml (ethylene glycol:water=50 vol. % 50vol. %) that contains dispersed multiwalled carbon nanotube (MWCNT) witha specific surface area of 30 m²/g of 0.5 g as a non-porous support. ANaOH solution was dropped, and the pH value of the solution was adjustedto 10 by using a pH litmus paper. In a nitrogen gas atmosphere, thesolution was stirred and refluxed for 4 hours at 130° C. so as todeposit PtP catalyst on the multiwalled carbon nanotube. After thereaction ends, filtration, washing, and drying were performed, therebyproducing catalyst.

EXAMPLE 43

Platinic hexachloride of hexahydrate of 1.69 mmol and sodiumhypophosphite of 0.845 mmol were dissolved into ethanol solution of 200ml (ethanol:water=50 vol. %:50 vol. %) and added to an ethanol solutionof 200 ml (ethanol:water=50 vol. %:50 vol. %) that contains dispersedmultiwalled carbon nanotube (MWCNT) with a specific surface area of 30m²/g of 0.5 g as a non-porous support. A NaOH solution was dropped, andthe pH value of the solution was adjusted to 10 by using a pH litmuspaper. In a nitrogen gas atmosphere, the solution was stirred andrefluxed for 4 hours at 95° C. so as to deposit PtP catalyst on themultiwalled carbon nanotube. After the reaction ends, filtration,washing, and drying were performed, thereby producing catalyst.

COMPARATIVE EXAMPLE 16

Bis(acetylacetonato)platinum(II) of 1.69 mmol was dissolved intoethylene glycol of 200 ml and added to an ethylene glycol solution of200 ml that contains dispersed multiwalled carbon nanotube (MWCNT) witha specific surface area of 30 m²/g of 0.5 g as a non-porous support. Asulfuric acid solution was dropped, and the pH value of the solution wasadjusted to 3 by using a pH litmus paper. In a nitrogen gas atmosphere,the solution was stirred and refluxed for 4 hours at 200° C. so as todeposit Pt catalyst on the multiwalled carbon nanotube. After thereaction ends, filtration, washing, and drying were performed, therebyproducing catalyst.

COMPARATIVE EXAMPLE 17

Bis(acetylacetonato)platinum(II) of 1.69 mmol was dissolved intoethylene glycol of 200 ml and added to an ethylene glycol solution of200 ml that contains dispersed acetylene black (AB) with a specificsurface area of 68 m²/g of 0.5 g as a non-porous support. A sulfuricacid solution was dropped, and the pH value of the solution was adjustedto 3 by using a pH litmus paper. In a nitrogen gas atmosphere, thesolution was stirred and refluxed for 4 hours at 200° C. so as todeposit Pt catalyst on the acetylene black. After the reaction ends,filtration, washing, and drying were performed, thereby producingcatalyst.

COMPARATIVE EXAMPLE 18

Bis(acetylacetonato)platinum(II) of 1.69 mmol was dissolved intoethylene glycol of 200 ml and added to an ethylene glycol solution of200 ml that contains dispersed carbon black (CB) with a specific surfacearea of 140 m²/g of 0.5 g as a porous support. A sulfuric acid solutionwas dropped, and the pH value of the solution was adjusted to 3 by usinga pH litmus paper. In a nitrogen gas atmosphere, the solution wasstirred and refluxed for 4 hours at 200° C. so as to deposit Pt catalyston the carbon black. After the reaction ends, filtration, washing, anddrying were performed, thereby producing catalyst.

The composition of each catalyst produced in Examples 24 to 43 andComparative Examples 16 to 18 is observed by X-ray photoelectronspectroscopy analysis (XPS). Further, the particle diameter of thecatalyst is observed by transmission electron microscope (TEM). Table 16shows the results. In examples 24 to 43, sodium hypophosphite or sodiumphosphate is added in a synthetic system and therefore P is added to thePt catalyst. The particle diameter of the PtP catalyst produced inExamples 24 to 41 decreases to 2 nm. Addition of P has the effect ofreducing the particle diameter of Pt catalyst to 2 nm even in the case anon-porous carbon support with a small specific surface area is used.Use of the non-porous carbon support with a small specific surface areaallows all catalyst to be deposited on the surface of the support, thusimproving catalyst utilization efficiency. Thus, adding P reduces thecatalyst particle diameter to 2 nm to keep high catalyst activity evenwhen a non-porous carbon support with a small specific surface area isused. The PtP catalyst is therefore an extremely useful catalystmaterial that can achieve high catalyst activity and high catalystutilization efficiency at the same time. Example 42 uses an ethyleneglycol aqueous solution as alcohol and synthesizes PtP catalyst bylowering a reflux temperature from 200° C. to 130° C. The growth of aparticle is suppressed by lowering the synthesis temperature. Thus, thePtP catalyst with a particle diameter of 1.8 nm is obtained by loweringthe synthesis temperature to 130° C. Similarly, Example 43 uses anethanol aqueous solution and synthesizes PtP catalyst at a refluxtemperature of 95° C. As a result, the PtP catalyst with a particlediameter of 1.5 nm is obtained. On the other hand, since ComparativeExamples 16 to 18 do not add P, the particle diameter of Pt catalyst isas large as 6 to 10 nm. Though the particle diameter of Pt catalystdecreases as a specific surface area of a carbon support increases, itis still as high as up to 6 nm even with a use of CB with a specificsurface area of 140 m²/g. TABLE 16 Support Catalyst specific particleCatalyst Carbon surface area diameter composition Catalyst support(m²/g) by TEM (at. %) Example 24 MWCNT 30 2 nm Pt₈₆P₁₄ Example 25 AB 682 nm Pt₈₆P₁₄ Example 26 CB 140 2 nm Pt₈₆P₁₄ Example 27 MWCNT 30 2 nmPt₈₇P₁₃ Example 28 AB 68 2 nm Pt₈₇P₁₃ Example 29 CB 140 2 nm Pt₈₇P₁₃Example 30 MWCNT 30 2 nm Pt₈₈P₁₂ Example 31 AB 68 2 nm Pt₈₈P₁₂ Example32 CB 140 2 nm Pt₈₈P₁₂ Example 33 MWCNT 30 2 nm Pt₈₉P₁₁ Example 34 AB 682 nm Pt₈₉P₁₁ Example 35 CB 140 2 nm Pt₈₉P₁₁ Example 36 MWCNT 30 2 nmPt₈₆P₁₄ Example 37 AB 68 2 nm Pt₈₆P₁₄ Example 38 CB 140 2 nm Pt₈₆P₁₄Example 39 MWCNT 30 2 nm Pt₈₅P₁₅ Example 40 AB 68 2 nm Pt₈₅P₁₅ Example41 CB 140 2 nm Pt₈₅P₁₅ Example 42 MWCNT 30 1.8 nm Pt₈₆P₁₄ Example 43MWCNT 30 1.5 nm Pt₈₆P₁₄ Comparative MWCNT 30 to 10 nm Pt₁₀₀ example 16Comparative AB 68 to 8 nm Pt₁₀₀ example 17 Comparative CB 140 to 6 nmPt₁₀₀ example 18

FIG. 7A shows a transmission electron microscope image of PtP catalystwith a multiwalled carbon nanotube support that is obtained by Example24, and FIG. 7B shows that of Pt catalyst with a multiwalled carbonnanotube support that is obtained by Comparative Example 24. As shown inthe images, the PtP catalyst of this invention has a particle diameterof 2 nm and catalyst particles are dispersed sufficiently. On the otherhand, the Pt catalyst of Comparative Example 24 that does not contain Phas a particle diameter of as large as up to 10 nm and catalystparticles are agglutinated and not dispersed sufficiently. These resultsshow the effects of reducing particle sizes and dispersing particles ofthe Pt catalyst by addition of P.

EXAMPLE 44

An alcohol solution of pure water and Nafion®, available from E.I.DuPont de Namours and Company, was added to the PtP catalyst with acarbon support that is obtained in Examples 24 to 43 and stirred, andthen its viscosity was adjusted to create a catalyst ink. The catalystink was then applied onto Teflon® sheet, available also from Dupont, insuch a way that the application amount of the PtP catalyst was 5 mg/cm².After dried, the Teflon® sheet was peeled off, thereby creating anoxygen electrode catalyst. Further, an alcohol solution of pure waterand Nafion® was added to the PtRuP catalyst with a particle diameter of2 nm supported on acetylene black (AB) with a specific surface area of68 m²/g, which is a non-porous carbon support, and stirred, and then itsviscosity was adjusted to create a catalyst ink. The catalyst ink wasthen applied onto Teflon® sheet in such a way that the amount of the Ptcatalyst was 5 mg/cm². After dried, the Teflon® sheet was peeled off,thereby creating a methanol electrode catalyst. Then, the PtP oxygenelectrode catalyst and the PtRuP methanol electrode catalyst were hotpressed to both sides of a polymer electrolyte membrane (Nafion®membrane 112, available from Dupont), thereby producing a membraneelectrode assembly. Using the membrane electrode assembly and a methanolsolution of 15 wt % as a liquid fuel, a direct methanol fuel cell shownin FIG. 4 was produced. The direct methanol fuel cell 10 of FIG. 4includes an oxygen electrode side charge collector 12, an oxygenelectrode side diffusion layer 14, a polymer electrolyte membrane 16, amethanol electrode side diffusion layer 18, a methanol electrode sidecharge collector 20, a methanol fuel tank 22, an air intake opening 24,an oxygen electrode PtP catalyst layer 26, a methanol electrode PtRuPcatalyst layer 28, and a methanol fuel intake opening 30. The oxygenelectrode side charge collector 12 serves as a structure to take in theair (oxygen) through the air intake opening 24 and also as a powercollector. The polymer electrolyte membrane 16 (Nafion® membrane 112,available from DuPont) serves as a carrier that carries proton generatedin the methanol electrode to the oxygen electrode and also as aseparator that prevents the short-circuit of the methanol electrode andthe oxygen electrode. In the direct methanol fuel cell 10 having thisconfiguration, liquid fuel supplied from the methanol electrode sidecharge collector 20 passes through the methanol electrode side diffusionlayer 18 and enters the methanol electrode catalyst layer 28 where it isoxidized into CO₂, electron, and proton. The proton passes through thepolymer electrolyte membrane 16 and moves to the oxygen electrode side.In the oxygen electrode, the oxygen entering from the oxygen electrodeside charge collector 12 is reduced by the electron generated in themethanol electrode, and this oxygen and the proton react to generatewater. The direct methanol fuel cell 10 of FIG. 4 generates electricpower by the methanol oxidation reaction and the oxygen reductionreaction.

EXAMPLE 45

The example 45 produced a direct methanol fuel cell in the same manneras Example 44 except for using the Pt catalyst of Comparative Examples16 to 18 instead of the PtP catalyst in Example 44 as oxygen electrodecatalyst.

The power density of each direct methanol fuel cell obtained in Example44 and 45 was measured. Table 17 shows the measurement results. SinceExample 44 used PtP catalyst, a catalyst particle diameter was 2 nm orless. Further, it used a non-porous carbon support or a carbon supportthat is a porous support with a relatively smaller number of fine poresas a catalyst support. Therefore, catalyst utilization efficiencyincreased as catalyst activity increased, and the power density was ashigh as 90 mW/cm² or higher. In Table 17, the power density was highestwith carbon support of MWCNT, second highest with AB and lowest with CB.The CB produced the lowest power density because CB is a porous supportand part of PtP catalyst was buried in the fine pores and unable tocontribute to oxygen reduction reaction. Since AB is a non-poroussupport, it produced a higher power density than the CB support. MWCNThad a large number of physical voids in the electrode catalyst layerbecause of being non-porous and its shape. This enhanced diffusion ofoxygen gas that served as fuel and water that was generated at cathode.Further, since MWCNT had a lower specific resistance than CB, it ispossible to reduce IR loss and suppress a decrease in cell voltage,thereby producing high power density. Furthermore, Example 42synthesized PtP catalyst by lowering a reflux temperature from 200° C.to 130° C., and Example 43 synthesized PtP catalyst by lowering a refluxtemperature to 95° C. The reduction in synthesis temperature suppressedgrowth of catalyst particles, and the particle diameters of PtP catalystwere reduced to 1.8 nm and 1.5 nm, respectively. The decrease inparticle diameter increased the specific surface area of catalyst toenhance catalyst activity, and the power density was thereby as high as110 mW/cm² or higher. On the other hand, as shown in Example 45, whenusing a non-porous MWCNT as a support, the particle diameter of Ptcatalyst, which does not contain P, was as large as up to 10 nm, and thepower density was 70 mW/cm². Even when CB with a large specific surfacearea was used as a support, the particle diameter was still as large asup to 6 nm and the power density increased by only about 5 mW/cm². TABLE17 Support specific Catalyst surface particle Catalyst Power Carbon areadiameter composition density Catalyst support (m²/g) (nm) (at. %)(mW/cm²) Example 24 MWCNT 30 2 Pt₈₆P₁₄ 100 Example 25 AB 68 2 Pt₈₆P₁₄ 95Example 26 CB 140 2 Pt₈₆P₁₄ 90 Example 27 MWCNT 30 2 Pt₈₇P₁₃ 101 Example28 AB 68 2 Pt₈₇P₁₃ 95 Example 29 CB 140 2 Pt₈₇P₁₃ 90 Example 30 MWCNT 302 Pt₈₈P₁₂ 102 Example 31 AB 68 2 Pt₈₈P₁₂ 96 Example 32 CB 140 2 Pt₈₈P₁₂90 Example 33 MWCNT 30 2 Pt₈₉P₁₁ 101 Example 34 AB 68 2 Pt₈₉P₁₁ 96Example 35 CB 140 2 Pt₈₉P₁₁ 90 Example 36 MWCNT 30 2 Pt₈₆P₁₄ 101 Example37 AB 68 2 Pt₈₆P₁₄ 94 Example 38 CB 140 2 Pt₈₆P₁₄ 90 Example 39 MWCNT 302 Pt₈₅P₁₅ 100 Example 40 AB 68 2 Pt₈₅P₁₅ 95 Example 41 CB 140 2 Pt₈₅P₁₅90 Example 42 MWCNT 30 1.8 Pt₈₆P₁₄ 110 Example 43 MWCNT 30 1.5 Pt₈₆P₁₄120 Comparative MWCNT 30  to 10 Pt₁₀₀ 70 example 16 Comparative AB 68 to8 Pt₁₀₀ 73 example 17 Comparative CB 140 to 6 Pt₁₀₀ 75 example 18

An alcohol solution of pure water and Nafion®, available from E.I.DuPont de Namours and Company, was added to the PtP catalyst with acarbon support that is obtained in Examples 24 to 43 and stirred, andthen its viscosity was adjusted to create a catalyst ink. The catalystink was then applied onto Teflon® sheet, available also from Dupont, insuch a way that the application amount of the PtP catalyst was 0.5mg/cm². After dried, the Teflon® sheet was peeled off, thereby creatingan oxygen electrode catalyst. Further, an alcohol solution of Nafion®and PtRuP catalyst with a particle diameter of 2 nm supported onacetylene black (AB) with a specific surface area of 68 m²/g, which is anon-porous carbon support were added and stirred, and then its viscositywas adjusted to create a catalyst ink. The catalyst ink was then appliedonto Teflon® sheet in such a way that the amount of the PtRuP catalystwas 0.5 mg/cm². After dried, the Teflon® sheet was peeled off, therebycreating a hydrogen electrode catalyst. Then, the PtP oxygen electrodecatalyst and the PtRuP hydrogen electrode catalyst were hot pressed toboth sides of a polymer electrolyte membrane (Nafion® membrane 112,available from Dupont), thereby producing a membrane electrode assembly.Using the membrane electrode assembly and hydrogen gas as fuel, apolymer electrolyte fuel cell shown in FIG. 5 was produced. The polymerelectrolyte fuel cell 40 of FIG. 5 includes an oxygen electrode sidecharge collector 44, an oxygen electrode side diffusion layer 43, apolymer electrolyte membrane 41, a hydrogen electrode side diffusionlayer 48, a hydrogen electrode side charge collector 47, an air intakeopening 42, an oxygen electrode PtP catalyst layer 45, a hydrogenelectrode PtRuP catalyst layer 46, and a hydrogen fuel intake opening49. The oxygen electrode side charge collector 44 serves as a structureto take in the air (oxygen) through the air intake opening 42 and alsoas a power collector. The polymer electrolyte membrane 41 (Nafion®membrane 112, available from DuPont) serves as a carrier that carriesproton generated in the hydrogen electrode to the oxygen electrode andalso as a separator that prevents the short-circuit of the hydrogenelectrode and the oxygen electrode. In the polymer electrolyte fuel cell40 having this configuration, the hydrogen gas supplied from thehydrogen electrode side charge collector 47 passes through the hydrogenelectrode side diffusion layer 48 and enters the hydrogen electrodecatalyst layer 46 where it is oxidized into electron and proton. Theproton passes through the polymer electrolyte membrane 41 and moves tothe oxygen electrode side. In the oxygen electrode, the oxygen enteringfrom the oxygen electrode side charge collector 44 is reduced by theelectron generated in the hydrogen electrode, and this oxygen and theproton react to generate water. The polymer electrolyte fuel cell 40 ofFIG. 5 generates electric power by the hydrogen oxidation reaction andthe oxygen reduction reaction.

EXAMPLE 47

The example 47 produced a polymer electrolyte fuel cell in the samemanner as Example 46 except for using the Pt catalyst produced inComparative Examples 16 to 18 instead of the PtP catalyst with a carbonsupport in Example 46 as oxygen electrode catalyst.

The power density of each polymer electrolyte fuel cell obtained inExample 46 and 47 was measured. Table 18 shows the measurement results.Since Example 46 used PtP catalyst, a catalyst particle diameter was 2nm or less. Further, it used a non-porous carbon support or a carbonsupport that is a porous support with a relatively smaller number offine pores as a catalyst support. Therefore, catalyst use efficiencyincreased as catalyst activity increased, and the power density was ashigh as 220 mW/cm² or higher. In Table 18, the power density was highestwith carbon support of MWCNT, second highest with AB and lowest with CB.The CB produced the lowest power density because CB is a porous supportand part of PtP catalyst was buried in the fine pores and unable tocontribute to oxygen reduction reaction. Since AB is a non-poroussupport, it produced a higher power density than the CB support. MWCNThad a large number of physical voids in the electrode catalyst layerbecause of being non-porous and its shape. This enhanced dispersion ofoxygen gas that served as fuel and water that was generated at cathode.Further, since MWCNT had a lower specific resistance than CB, it ispossible to reduce IR loss and suppress a decrease in cell voltage,thereby producing high power density. Furthermore, Example 42synthesized PtP catalyst by lowering a reflux temperature from 200° C.to 130° C., and Example 43 synthesized PtP catalyst by lowering a refluxtemperature to 95° C. The reduction in synthesis temperature suppressedgrowth of catalyst particles, and the particle diameters of PtP catalystwere reduced to 1.8 nm and 1.5 nm, respectively. The decrease inparticle diameter increased the specific surface area of catalyst toenhance catalyst activity, and the power density was thereby as high as240 mW/cm² or higher. On the other hand, as shown in Example 47, whenusing a non-porous MWCNT as a support, the particle diameter of Ptcatalyst, which does not contain P, was as large as up to 10 nm, and thepower density was 180 mW/cm2 Even when CB with a large specific surfacearea was used as a support, the particle diameter was still as large asup to 6 nm and the power density increased by only about 10 mW/cm².TABLE 18 Support specific Catalyst surface particle Catalyst PowerCarbon area diameter composition density Catalyst support (m²/g) (nm)(at. %) (mW/cm²) Example 24 MWCNT 30 2 Pt₈₆P₁₄ 230 Example 25 AB 68 2Pt₈₆P₁₄ 225 Example 26 CB 140 2 Pt₈₆P₁₄ 220 Example 27 MWCNT 30 2Pt₈₇P₁₃ 230 Example 28 AB 68 2 Pt₈₇P₁₃ 226 Example 29 CB 140 2 Pt₈₇P₁₃220 Example 30 MWCNT 30 2 Pt₈₈P₁₂ 231 Example 31 AB 68 2 Pt₈₈P₁₂ 225Example 32 CB 140 2 Pt₈₈P₁₂ 220 Example 33 MWCNT 30 2 Pt₈₉P₁₁ 231Example 34 AB 68 2 Pt₈₉P₁₁ 226 Example 35 CB 140 2 Pt₈₉P₁₁ 220 Example36 MWCNT 30 2 Pt₈₆P₁₄ 232 Example 37 AB 68 2 Pt₈₆P₁₄ 227 Example 38 CB140 2 Pt₈₆P₁₄ 220 Example 39 MWCNT 30 2 Pt₈₅P₁₅ 230 Example 40 AR 68 2Pt₈₅P₁₅ 225 Example 41 CB 140 2 Pt₈₅P₁₅ 220 Example 42 MWCNT 30 1.8Pt₈₆P₁₄ 240 Example 43 MWCNT 30 1.5 Pt₈₆P₁₄ 250 Comparative MWCNT 30  to10 Pt₁₀₀ 180 example 16 Comparative AB 68 to 8 Pt₁₀₀ 185 example 17Comparative CB 140 to 6 Pt₁₀₀ 190 example 18

EXAMPLE 48

Bis(acetylacetonato)platinum(II) of 1.69 mmol was dissolved intoethylene glycol of 100 ml and mixed together. Sodium hypophosphite of 0to 200 mol % of the number of Pt moles was then dissolved into ethyleneglycol solution of 100 ml and added to the above solution. Further,ethylene glycol solution of 200 ml where multiwalled carbon nanotube(MWCNT) with a specific surface area of 30 m²/g, which is a non-poroussupport, of 0.5 g was dispersed was added thereto. A sulfuric acidsolution was dropped into this solution, and the pH value was adjustedto 3 by using a pH litmus paper. In a nitrogen gas atmosphere, thesolution was stirred and refluxed in an oil bath at 200° C. for 4 hours,thereby depositing PtP catalyst on the multiwalled carbon nanotube.After the reaction ended, filtration, washing, and drying wereperformed, thereby producing catalyst.

X-ray diffraction analysis was performed on the PtP catalyst obtained inExample 48, and the particle diameter of the PtP catalyst was estimatedby applying the Scherrer's formula to the diffraction peak of (220).Then, the composition of the catalyst was observed by XPS. Further, adirect methanol fuel cell was produced with the PtP catalyst in thesimilar manner as Example 44 and the power density of each cell wasmeasured. Table 19 shows the results. It shows that if the content of Pis 2at. % or higher, the particle diameter of the PtP catalyst isreduced to less than 3 nm and achieves high power density. On the otherhand, if the content of P exceeds 50at. %, the content of Pt decreasesto reduce the power density. TABLE 19 Amount of Catalyst sodium particleCatalyst Power hypophosphite diameter composition density added (nm)(at. %) (mW/cm²)  0 mol % to 10 Pt₁₀₀ 70  5 mol % 2.4 Pt₉₇P₃ 85  10 mol% 2.2 Pt₉₅P₅ 88  20 mol % 2.1 Pt₈₁P₉ 94  50 mol % 2.0 Pt₈₆P₁₄ 100 100mol % 2.0 Pt₇₈P₂₂ 110 150 mol % 1.8 Pt₇₂P₂₈ 103 200 mol % 1.6 Pt₄₇P₅₃ 70

The catalyst composed of PtP may be used as oxygen electrode catalyst ofa direct methanol fuel cell (DMFC) and a polymer electrolyte fuel cell(PEFC). It may be also used as an oxygen electrode catalyst layer in amembrane electrode assembly for these fuel cells. The PtP catalyst ofthe present invention has hydrogen oxidation activity and it may be usedas hydrogen electrode catalyst of a polymer electrolyte fuel cell thatuses pure hydrogen with no CO poisoning as fuel.

Though the catalyst for fuel cell composed of Pt—Ru—P particulatesdeposited on a carbon support of this invention is particularly suitablefor use in direct methanol fuel cells, it may be used also as a catalystof polymer electrolyte fuel cells.

From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

1. A heterogeneous catalyst comprising Pt particles, wherein said Ptparticles comprise P as additive.
 2. The heterogeneous catalystaccording to claim 1, wherein said Pt particles having a diameter from 1to 3 nm.
 3. The heterogeneous catalyst according to claim 1, whereinsaid Pt particles comprise at least 2 atom % P.
 4. The heterogeneouscatalyst according to claim 1, wherein the content of P is 2 atom % to50 atom %.
 5. The heterogeneous catalyst according to claim 1, furthercomprising a carbon support.
 6. The heterogeneous catalyst according toclaim 5, wherein the carbon support is at least one selected from thegroup consisting of carbon black and carbon nanotube.
 7. Theheterogeneous catalyst according to claim 6, wherein the carbon supportis a multi-walled carbon nanotube.
 8. The heterogeneous catalystaccording to claim 1, wherein each particle comprise Pt, Ru and P. 9.The heterogeneous catalyst according to claim 8, wherein the ratio of Ptand Ru in the particles is Pt₄₀Ru₆₀ to Pt₉₀Ru₁₀.
 10. The heterogeneouscatalyst according to claim 5, further comprising a carbon supporthaving a specific surface area in a range of 20 m²/g to 300 m²/g. 11.The heterogeneous catalyst according to claim 8, wherein the content ofP is 3 atom % to 27 atom % of the total moles of Pt—Ru.
 12. A fuel cellcomprising: a cathode, an anode and a polymer electrolyte membraneplaced between the cathode and anode, wherein said cathode and/or anodecomprise said catalyst according to claim
 1. 13. A fuel cell comprising:a cathode, an anode and a polymer electrolyte membrane placed betweenthe cathode and anode, wherein said cathode comprise said catalystaccording to claim
 1. 14. A fuel cell comprising: a cathode, an anodeand a polymer electrolyte membrane placed between the cathode and anode,wherein said anode comprise said catalyst according to claim
 8. 15. Afuel cell comprising: a cathode, an anode and a polymer electrolytemembrane placed between the cathode and anode, wherein said cathodecomprise said catalyst according to claim 1, and said anode comprisesaid catalyst according to claim
 8. 16. A process for preparing thecatalyst according to claim 1, comprising: a step for reducing Pt ionsin the presence of reducing agent comprising phosphorus.
 17. The processaccording to claim 16, wherein the compound derives from one ofphosphinic acid or phosphonic acid.
 18. The process according to claim16, wherein the reducing step is an alcohol reduction or electrolessplating step.
 19. A process for preparing the catalyst according toclaim 8, comprising: a step for reducing Pt ions in the presence ofreducing agent comprising phosphorus.
 20. A membrane electrode assembly,comprising: an anode catalyst layer, a cathode catalyst layer and apolymer electrolyte membrane placed between the anode catalyst layer andthe cathode catalyst layer wherein said anode catalyst layer and/orcathode catalyst layer comprise said catalyst according to claim
 1. 21.A membrane electrode assembly, comprising: an anode catalyst layer, acathode catalyst layer and a polymer electrolyte membrane placed betweenthe anode catalyst layer and the cathode catalyst layer wherein saidcathode catalyst layer comprise said catalyst according to claim
 1. 22.A membrane electrode assembly, comprising: an anode catalyst layer, acathode catalyst layer and a polymer electrolyte membrane placed betweenthe anode catalyst layer and the cathode catalyst layer wherein saidanode catalyst layer comprise said catalyst according to claim
 8. 23.The method of producing a voltage with the fuel cell according to claim12 comprising: feeding methanol and water, or hydrogen to the anode andfeeding oxygen to the cathode.